Oh yeah, of course! Consider this all notes for down the line as things shape up----new content and twists months after the fact help things stay lively afterall.
Specifics like drowning could easily be wrangled down the line...way down the line. I could see drowning something of an instant kill on foes of substantially greater than human size since, well, you can see what'd happen----would be a notion for the crafty to take down the overwhelmingly robust in melee.
Hmm...interesting on the D&D rule notion, though since this isn't striving to the letter of the law, so to speak, perhaps "something" of this notion could be taken to heart. For instance, perhaps a temp "mod" relative to what is happening? Like, an enemy wizard summons a Water Elemental. Your party doesn't happen to have any resistant gear to Water...so things are looking dicey. Taking a chance on your Fighter, you cast a freezing spell of some sort at the water summon. While it does no direct damage, it does slow the movement rate to something more logical. Furthermore, as it temporarily has a more physical form, it then does physical/blunt damage instead of Water, as well as making it easier to hit for one's fighter. Nothing to say it couldn't still beat the Fighter to death if enough went wrong, thaw out, then waylay the rest of the party, BUT, it'd be something nifty. Or something more tangential like if you can destroy an enemy Fire summon with a strong Water spell it will erupt into a cloud of steam which might damage and/or hinder the sight and such of the enemy party that was trying to wade into battle with it in tow.