Out of interest, how would a space suit go under water in real life?
It
could go, but it's not designed to.
I too agree the oxygen gears should support the player underwater (it seems most players expect this), but still it would not suit best for underwater activities or movement. The player would be required to add/use some kind of "Depth Strider" module or attachment to facilitate the underwater use. Also to make more sense, Galacticraft needs to feature a "watery" planet, then we could implement an underwater system and make the oxygen gears work underwater too.... you know why, Galacticraft is not a scuba mod.
I know space suits are not designed to be used underwater in real life, but I tend to place players' expectations before realism.
EDIT: I'll merge this topic to a suggetion topic once this is not a bug.