A few thoughts/comments (in no particular order):
In the real world, we are spending big money on additional platform capacity at Forster Square for London trains to have a platform to recover at/ wait until it's time to head back to Leeds, currently they can sit for over an hour in Bradford. Similarly the existing GC service can sit at t'Interchange for most of an hour. For example, at the moment there's an LNER service sat in Bradford from 13:55-15:16 midweek with a GC service occupying a platform across town between 14:02-14:49. So two city centre platforms tied up for quite a while at the same time and probably no scope to realistically cut either of those (given recovery/ cleaning/ staff layovers/ finding suitable paths for long distance trains)
(There's currently similar need to give Shipley EMUs somewhere to sit off-peak - rather than occupy scarce platform capacity in Leeds or take up Neville Hill paths - a future Shipley depot will hopefully give the EMUs somewhere else to lay over, in theory, but...)
Any "central" station in Bradford would presumably need to be built with plenty of "spare" platforms for such eventualities, especially since you'd probably not be able to extend your site once built, especially if it's underground/viaduct. Which makes it at least three platforms just for trains to lay over for long periods... Plus at least two, maybe four through platforms to accommodate the current Northern services (given contingency for disruption/ freight/ breakdowns/ crew changes etc on "local" services)?
Do you need to throw in any more capacity to allow diverted TPE services? Maybe even some Carlisle/ Morecambe trains? Don't forget the all-important services to East Lancashire via Skipton and Colne, that some seem convinced will happen... Okay, not everything will happen, but it would be very "brave" to design this scheme to accommodate just six trains an hour in each direction when touting all these other supposed benefits, given the Bradford ambitions (remember the desire for through Nottingham/ Manchester Airport trains?).
And that's in a railway industry that already seems to pay through the nose for any infrastructure even for the most basic new station (or accessible toilet!). As well as space for trams? And a decent sized station with long platforms if Bradford gets a station on a 'fast' Leeds-Manchester line?
Plus presumably at least one more brand new through station in the city centre, to avoid disadvantaging existing passengers (that will similarly need more than two platforms, to allow overtaking etc)? If you want to future-proof it then you don't want to make the mistakes that British Rail did in the 1980s when designing stations like Meadowhall (just a two shortish platforms on each line , meaning no scope for XC/ London trains to either stop or overtake there, can't even fit much more than a four car Sprinter, even TPE have to use SDO there, can't use it for daytime services to terminate).
Don't want to create another Castlefield, where various long distance trains are significantly delayed because trying to squeeze a mish-mash of through routes coming from different directions with no scope for the slightest disruption... The Elizabeth Line can cope with high frequencies on a two track line because it's a simple service pattern/ map. Try doing the same on a two track line with York/ Hull/ London/ Blackpool/ Wigan/ Chester etc trains ( plus freight?)... A billion here, a billion there, pretty soon, you're talking real money, as the saying goes...
There's a finite number of paths into/ platforms at Leeds. Look at how expensive the costs are for a short extension to the single platform (17) that has to cope with four terminating trains each hour that means the Nottingham service is stuck at just two coaches)? Leeds isn't going to get those HS2 platforms to free up existing platform space, in fact Leeds capacity would probably benefit from dumping trains at Bradford to get them out of the way.
At the moment, Bradford had two and a half services an hour via Shipley, and four via Pudsey. Since the LNER trains aren't realistically going to be extended along the Calder Valley onto Manchester in place of existing Northern DMUs (or run straight back out to London via Leeds with no more than a two minute dwell in Bradford!), you realistically have to plan Northern services around six Leeds paths an hour
Halifax currently has four direct Leeds trains each hour, two of which are from Manchester, one from Blackpool (so three from Hebden Bridge that route, not counting the Calder Valley service via Brighouse). Fun though Leeds-Bradford-Leeds shuttles may sound, or extending the Skipton/Ilkley services through Pudsey to Leeds looks good to members of the Bufferphobic community (not sure anyone is going to sit on a train from Ilkley to Leeds that goes via Bradford, so not sure what benefit there'd be from that, you don't want reliability at Leeds to be at the mercy of half hourly trains along the single track section between Guisley and Shipley)
So does that mean halving the Halifax frequency to Leeds? Can't see that going down well.
Or would your plan be for two of the Halifax services to run via Shipley into Leeds whilst the four Pudsey paths are taken by an extension of Skipton services beyond Bradford and the other two Halifax services continuing to reverse in Bradford to follow their existing route into Leeds ( and the Ilkley trains terminate in central Bradford)? Bang goes any claim that reversal takes too long as justification for why we need to spend huge sums on a through station then.
In terms of speeding up longer distance trains, there's the problem that paths might not tie up particularly well between the fixed slots at busy junctions, so dwell times might have to be extended rather than cut (e.g. if you want a Blackpool - York train to run via Shipley to avoid reversal then will it slot neatly through the fixed path at Armley? Any slight delay may mean it loses it's slots further afield (e.g. if it needs to stop at multiple Bradford stations plus get a path between Harrogate services could lose it a slot though Neville Hill or at Preston), meaning journey times extended further
Or we hope paths on the Transpennine line allow us to double the Huddersfield frequency to create a half hourly Ilkley-Huddersfield train that somehow fits with platform capacity at Huddersfield / TPE paths through Deighton/ the single track section through Baildon? If not then that's even more platforms needed in central Bradford to accommodate terminating services.
But then the idea of Manchester/Blackpool services avoiding central Bradford (serving a station on the edge of East Bowling instead, maybe with a tram connection?) seems incredibly unpopular in the city. Diverting via an East Bowling station (and avoiding the city centre) would certainly save time on journeys like Blackpool-Leeds, but I thought it was unacceptable to central Bradford to lose their Manchester trains?
Then there's electrification to consider. Does the plan include wiring the Calder Valley too? All the way to Manchester/ Preston? And the line through Pudsey? Obviously bi-modes mean that's not as necessary as it once would have been, that'll mean a few quid on new trains too, given how many units are going to pass through Bradford each hour in this scenario (running from Halifax/York to Blackpool/Wigan/ Chester plus potentially Skipton etc too?)!
It does sound fun to model in OO gauge though, a fictional world where a busy city station sees a variety of local/ long distance services. A chance to mix trains from different lines into one station, maybe with the excuse of 'diverted services from the S&C/ Transpennine' too, to throw in for fun. Just a waste of resources (and crayons) in real life.
