I think the .303 Enfield is a great piece of history akin with the 30'06 Garand and Springfields and 8mm mausers.
I think 8mm rifles will share the same fate as the .303 once the surplus supply of Yugo 8mm runs out (get it while you can!).
Unfortunately, the lack of surplus ammo has probably forever stablized the prices of surplus .303 rifles since very few folks have the time or energy to reload. Only the few dedicated collectors will bother.
Perhaps someone will find a hidden stash of ammo in Pakistan or India but I don't forsee the .303 being popular again.