1 - I sincerely hope that the Didcot/Oxford shuttle is only temporary. Indeed I understood the rationale of the bi-mode/trimode was to restore a proper full stopping service all the way between Reading and Oxford, mitigating the adverse impact of the dreadful decision to cut the electrification to Oxford short at Didcot.
2 - I am not so sure that the case for trains beyond Oxford all going west to Swindon/Bristol etc is strong. The potential passenger traffic from the Reading/Basingstoke/Winchester/Southampton/Bournemouth axis surely justifies a substantial part of any southward traffic going east. Reading alone generates considerable volume, and more capacity might encourage more to take the train not the car. I have over the years had a number of regular meeting commitments in Norfolk and Cambridgeshire and used the car to avoid the hassle of crossing London by tube at peak times.
1 - From what I’ve so far heard, the Tri-mode 769s will not be used on services to Oxford. They will be used on Reading to Gatwick trains as well as covering for the loss of 387s to Heathrow Express on the Paddington to Didcot services, as well as possibly some of the Thames Valley branches. That of course may not be the current plan, or it may be the current plan but will change. I’ll see if I can find out.
2 - For me, the problem with Reading as a destination is that it is either a new service calling at Didcot and Reading, or it somehow absorbs the current stopping services between Oxford and Didcot and Didcot and Reading. You will have problems finding paths for the former, and journey times will be badly compromised to/from Reading if the latter - don’t forget Crossrail will make certain cross London transfers easier, though not Milton Keynes admittedly.
Also if you send a train to Reading to terminate then it takes up valuable platform time until it heads back again. Send it onwards from Reading somewhere might work, but nowhere immediately springs to mind.
Send them west to Bristol and you open up all sorts of new through train markets.
The best compromise in terms of being a little more adventurous might be to run a Reading/Didcot to Milton Keynes train each hour and a Bristol to Bedford one each hour (not necessarily calling at Didcot).
Plenty of options on the table, let’s hope there’s a bit of imaginative thinking.