The Sig Cross is already in the game.
Anything too big will make no sense from a balancing perspective. It should stay under .338 Lapua/Norma. The only exception I could see possibly working is a single shot 50 like a Barret M99. Personally I'd prefer the M95 like in the old battlefields, but balancing would be tough. You could make the gun cycle slowly, which would be accurate to real life. I own a real Barrett M95 and, I'll tell ya, a bulpup 50 is extrordinarily uncomfortable to shoot.
I agree on the AXSR, though it will (or should) be identical to the MRAD. A Sako TRG M10 (absolutely fantastic trigger IRL) would be cool too
I'd like to see proper balancing of what is already there first. 300NM is faster than 300WM so why is the MRAD slower than the Remington 2010, and why is the Sig Cross (6.5CM?) as fast or faster than both? 300NM is also ballistically superior so why does it have significanly more drop? Most importantly, the LASER RANGEFINDER SHOULDNT ZERO YOUR SCOPE and there should be 12x (or maybe 16x) scopes available to make long range sniping fun again.