Consider what elements of gameplay you remove, and if something can be modified to maintain the deep (lol) gameplay :
- Light sources (flares) : The gameplay of throwing flares around can easily be replaced by a one-handed flare gun which shoots 1-tile incendiary ammo. (I've experimented with it, it's quite fun) Or allow the engine to create a "permanent" (non-recoverable) lightsource item at the point of impact : Aquanauts fire darts with flares affixed to them.
- Proximity mines : If you can only drop them at your feet, you're dead
You can keep them usable if you let soldiers toss them at 2 tiles (and never undershoot!), or if the "Prime" automatically drops them but they activate only at end of turn.
- Smoke grenades : They are much less efficient if you can't create the entire cloud between you and the enemy. This can be compensated by making a bigger cloud, and/or a smoke physics in water which actually expands over time.
- Sharing items between soldiers : If you prohibit throwing, the giver has to drop and walk away. Allowing soldiers to throw 1 tile feels much more comfortable.
- All kind of grenades : Compared to one-shot explosive ammo, they have the specificity that they allow attack without line of sight. I can't think of an equivalent....
- Grenade chain : gets completely removed. It's a pity because it was a smart trick which really involved cooperation of several soldiers.