Most acid maps already have startboxes that don't contain acid. Make a ticket with a list or something if there are some that don't, patching any stragglers would be good.
Maybe plop could fail to happen in acid or lava. The fac nanoframe will start taking damage immediately so it should be fairly obvious why the plop failed.
Making the graphics work pre-game (regardless of if it's a shader, LUPS, or anything else) would still be good regardless of the two above because there is no reason to keep useful graphical feedback away from the player. The current reason is technical (CEGs are synced).
"acid should be a shader and not a particle" pretty much
Acid should be unsynced and not synced. LUPS is a particle but is unsynced so I think it would work well to achieve the goal of working pre-game. A shader would probably look better than LUPS but costs more mana.