I don't expect him to be improved. I expect to see Philo play the whole game. Anyone who thinks Key will hold Philo out to save his RS doesn't realize yet that it's all about today. Don't worry about tomorrow, because tomorrow may never come.
I remember Leo Mazzone on the radio discussing a baseball team that was still in the playoff hunt, but decently behind. As I recall the discussion, the team was missing one piece to be a very good team. The others asked Leo if it would make sense to give up on that season and make trades to get what they need for the next year. Mazzone said, you never give up on right now while you have an opportunity. That it might look good on paper to get the one piece you need for next year, but there are no guarantees that you will still have everything else. You might get that one piece, but then lose several other pieces that are giving you the chance this year.
Like you said, tomorrow may never come. Philo could transfer. Philo could get hurt. (I hope neither happens) GT could have as many OL injuries in Philo's RS Senior season as GT had in 2015. Philo could get drafted after 2026, and not play in his RS Junior nor RS Senior year. There could be a pandemic or terrorist event that stops the entire season his RS Senior year. If the best chance to beat the mutts is to start Philo, then he starts. If the best chance to beat the mutts is to play Philo a few plays in the game, then he plays a few plays. If the best chance to beat the mutts is to play King and use Philo only in an emergency situation, then they will do that. What you do not do is forfeit the mutt game in order to keep open a chance that Philo might play in 2028.