The Networkers are meant to be replaced in the next franchise (if it ever happens!). Hitachi were front runners for that. Chiltern will need new stock, both additional and indeed to replace the 165s. East West rail will need trains from somewhere.
Then there are the trains for HS2 as well...
HS2 is basically a done deal already though isn't it. Theres only really alstom and hitachi in the race.
Talgo still a bit new to the UK so probably too much of a risk for such a high profile project,although they might be in with a shout for scotrail HST replacement
as for chiltern,I would think the 165's would end up at GWR, the 168's to East west rail, and the new chiltern DMU fleet still to be confirmed.
We've not had much of a look at hitachi DMU's yet, much as I'd like to see them keep it in house here in the UK and pair up with some cummins engines(locally built in darlington IIRC), it would likely end up a hitachi/MTU partnership.
Bombardier we thought had lost interest in DMU manufacture, but they are developing hybrid power packs now.Maybe they will express intent to bid after all.
Stadler and CAF would appear to be the most likely beneficiary of orders from chiltern,and also for replacement of sprinters in general.
for the sake of uniformity/interoperability, the 15x fleet needs to be looked at as a single entity when it's replaced.There's nothing inherently wrong with the basic design of them for the tasks they are required to do,so the new builder should bear that in mind.They just need to be super economical,go anywhere unrestricted,end gangway for occasional larger diagrams and 90mph capable throughout.
Bells and whislts like PRM,Aircon and wifi are pretty much a given now on all new products