Yes! I agree! I feel like the current XP reward system can sometimes feel rather harsh. I can definitely see this system being a nice addition to some other gamemodes too!
The only possible problem I can think of, is the impact this would have on camping. If higher placements are rewarded with XP, then that would reward camping, which is not ideal.
I also think it would be nice to reward kills. In Eggwars, perhaps this should be final kills/ egg breaks instead (as to not encourage farming kills).