Very true but think about the newer commuters too.
I don't think anyone needs to be a genius to work out which large city is located to the east of Reading... whether they have just started commuting or not and, as a result, where all the trains are going to end up. People aren't stupid. They can work out for themselves what's going on, they talk to fellow commuters, etc.
I think the real trick would be to install the additional crossover to the west of Reading so these trains can cross over from the up relief and be fed, along with the other longer distance trains into the #10/#11 island, the de facto 'fast London' platform, so when emus appear they just form the 'next fast' to London and will largely empty the platform in the process. Such additional trackwork, removing some traffic from the relief side will also make accommodating greater terminating traffic from the east much easier to plan and deliver (i.e. potentially up to 4 TPH Elizabeth Line as well as similar quantities of Heathrow western connection services (although the latter would be better extended to local destinations west of Reading I believe).
I doubt 10 and 11 could handle any more trains - they're already busy enough and moving trains across from the relief line would cause conflicts with westbound relief line services, freights heading to the Berks & Hants, etc - the whole point of rebuilding Reading station and adding the flyover and altering the junctions to the west was to remove conflicts.
In addition, switching the Didcot limited-stop 387 services to/from the main lines at Maidenhead or other places to the east makes the best use of the capacity available on the reliefs and allows trains arriving from the London direction to be sorted out well to the east of Reading.
I've said it before, so I'll say it again - is it so hard for all the people here with 'solutions' to just wait and see what impact the introduction of the 387s and 800s, with their extra seats, the new GWR timetable in 12 months' time and Crossrail reaching Reading in December 2019 have on the situation?
All that adds up to a huge increase in capacity for the Thames Valley, even before you get to the likely changes to travel habits that Crossrail will permit, by offering direct access to central London and the City. It may just turn out that they do the trick all by themselves, without barriers, armies of staff policing commuters, etc, etc, etc...
As we can see, reddragon's journey habits have already been changed just by the first phase of 387 operation west of Maidenhead.