Here me out
What if Archer EMIYA had somehow been released from his contract with Alaya and was reborn back in time as his young self.
With this second chance he can fix the things that he regrets like not being able to save Sabers Heart.
Find someone to help Illya.
Deal with Zouken and Save Sakura.
Have a love life with Rin.
Pay more attention to his loved ones instead of his old dream of being a hero of Justice.
Emiya Alter Story:
I always found it kind of disappointing not seeing the Shirou Emiya of Prisma Illya being able to use his powers and kind of just there as a comic relief.
So, I thought what if he just so happened to find the archer card containing the spirt of EMIYA Alter.