ok, before you go, "pron wouldn't work go read the DNSL" or something like that, i have a few ideas for how it would work without being stupidly annoying to other players.
You can only shoot if you aren't moving.
You can use your shovel to dig 1x1 tunnels.
but the delay between hits has to be higher, because it would be harder to use a shover in that confined space.
no sprinting. slow pace. you can't swim prone.
less recoil than crouching. same accuracy.
max player height is 1 block, that way you chould get some cover behind 1x1 blocks.
when you go prone your gun has to take at least 3 seconds to get into position. so those moments where ur shooting people then they go prone, then they shoot you; wont happen so easily.
The idea, is for it to be a last resort for when your cover gets blown down.