As much as I'd like to see the 442's back with SWT, they wouldn't be able to be used on the Weymouth line as 24 units isn't enough to cover the diagrams complete.
If they came back, they'd have to be massively upgraded below the floor. New traction motors and also associated traction equipment - I believe quite a bit was recycled from the REP's.
Even if this was feasible - and the cost would be quite high - are there traction motors out there with the equivalent power (if not a bit more to give better acceleration) to replace the ex-REP traction motors?
The next issue is that the doors are probably a bit too narrow. Performance is key, and SWT would not want to take on a unit that could have longer dwell times than even a 444. So I'd suggest a Chiltern style upgrade (that uses the 444 door mechanism). Whilst still narrow in comparison to a 450, at least with a new mechanism the doors would open/close quicker.
Interior wise you'd need a high capacity interior. Whilst not to everyone's tastes, FGW has shown what can be done with the Mark 3. So whilst Chilternisation of the vestibules would eat into the saloon a little, I believe that with no luggage stacks and one toilet per trailer, it would be possible to seat 82/84 in the trailers. The Motor coach is pretty much open now, apart from the Guards saloon. The former DTCsoL could be fitted out with 36 First Class seats, a universal loo and two wheelchair spaces, plus a handful of standard seats. I believe that it would be possible to get a 10-car train that would seat the same number of First Class passengers as a 12-car 450 and 40-50 less Standard Class passengers.
So where could SWT use 24 such units? My only suggestion would be the fast Waterloo-Portsmouth services. The problem is that whilst having these units on the Portsmouth line might be popular with passengers - and offer more capacity than a 10-car 444 - I'm not sure the DfT would accept it, as it would be a loss of capacity on the Portsmouth line. Love or hate 450's, on paper they offer more seats - whether used or not.