I think you can pencil in Saka, Bellingham, Rice, Shaw (chance for Chilwell but Shaw has probably been the #1 player throughout Southgate's reign, along with Kane), Stones and Reece James. So the clearest battles are:
Serious Battles:
Foden vs Rashford vs Every Other Winger - Easiest position for young players to break into since pace is so vital, but tough to see past these 2 with Sterling unlikely to improve and those 2 with a bit of time on their side to peak.
Foden vs Maddison vs Ramsey vs Gallagher vs Mount - Maddison would be helped by Toney being the 9 over Kane since Kane drops into the 10 spot a lot, whereas conversely, Ramsey and Gallagher's box to box abilities in the half-space mean they want Kane to stay healthy and not lose a couple steps over the next 18 months. This spot probably doesn't get settled by tournament's start, though Ramsay might grow a ton under Emery and he fits England's goal of basically becoming a France type team that wins with power first and foremost. Maddison has to improve his defensive game, so he might need a move as well, if he could go to say Liverpool or Spurs and win a starting role that would help (be tough with Conte, but if he was good enough he might relegate Kulusevski to RWB and the odd start in a 3-4-2-1), or be a star at Newcastle I guess.
Ramsdale vs Pickford - Henderson has the best penalty record, so he may be the 3rd keeper who comes on to save those, but for the starter I'd say Ramsdale is the slight favorite, and I wouldn't rule out a serious controversy here as Pickford hasn't really done anything to lose the job and might feel aggrieved, but Ramsdale is playing for a good team and is a better passer and just seems like he has more upside.
Guehi vs Colwill vs Maguire vs Tomori vs White vs Chalobah- White would have to get an injury to an Arsenal CB or Southgate really has to commit to him right away as the first choice LCB and hope he and Stones form a nice partnership at international level. Guehi actually plays there and England could use some pace at the back, especially with Walker likely aging into a backup. Colwill seems highly rated and left-footed and a passer, and I could see Potter starting him in the opening game of next season and never looking back, in which case he'd be in with a shout. Maguire needs a move most likely, but he also could just play well with Varane inevitably injured. Most likely though he needs to go to West Ham and look really good again with a deep line.
A Firm Favorite:
Kane vs Toney vs Abraham and all other #9s - Will Kane decline? If he doesn't it's his spot, but Toney might get a big move and big target men strikers who win things in the air are always useful in the chaos of international football without attacking patterns really being a thing. This is probably more of a 2026 question when Kane is 32/33, though we'll see how healthy he stays.