For me, honestly, not many.
It feels harder for defenders anyway - can be bullied by experienced strikers.
I like Riley Harbottle and Tyrese Fornah, but they are both over 21, so would have to be part of the 25. But that's fairly unlikely. Given how hard we found the division initially, I'd be surprised if we put faith in relatively untried players in the 25 next season (look at the January signings for example, predominantly proven players).
Of the current U21s, I really like 19-year-old Jamie McDonnell Supposedly a midfielder, but has played a lot at CB. Travelled with the first-team to Chelsea or Palace I think.
I'd like to see Donnelly/Taylor get loans at good Championship sides, after successful loans in L1 last season.
The Hammond brothers (Oli and Ben) look to have a bright future as well.
Oli, still only 20, is a great player, has something of the Frank Lampard about him - creates goals, arrives in the box late and scores quite a few too. However, still looks a bit lightweight at present, but could fill the Lingard gap on the bench. Probably needs a loan though, given he missed out in January as we were short on midfield cover at the time.
Fin Back is also still only 20, while Alex Mighten is only just 21, so they wouldn't count in the 25 and already have first-team experience.
If Clarridge stays fit I'd expect him to feature in the League Cup and possibly make the bench going forward.
There are quite U21 players who are under contract, but are 22 already, so would have to count in the 25. They may feature pre-season, but I expect the likes of Larsson, Konate to be allowed to go if someone comes in for them.