I dont think it's worth it to change versions, and here's why:
You can already log on in 1.16, if you want the certain combat styles or the lower shifting or whatnot
The only thing that would be really applicable in my opinion would be the certain nether blocks, which would look entirely different to someone on 1.15 and below
This would give 1.8 players an even greater advantage in PvP and PvP related events
If it was solely 1.16 based, you wouldn't be able to switch game modes, leading a ton of people who quit because of it. This would evidently mean a lower player count- making the change essentially pointless
So overall, in my opinion, it is better to just stay where we are, with not too many block/mob changes, and have the small number of people who are really set on a 1.16 server to go to Munchy or a different server that is 1.16 based