Would be nice for creating water/fog effects in mods.

This is a good idea

It'll probably also raise the cap on number of objects placable as I'm assuming that pass-through objects won't lag the game as much as solid objects

Yes. Objects that are visible but with 0 resistance, so you can freely pass through them.

yeah, this seems nice.

pass-through water/fog looks better with transparency, too.

Yeah this idea is very cool, this might make parkouring a bit more fun

if you're looking for water physics, there's a script by Yoyo that makes it possible

however I'm still all for intangible objects, gives a new dynamic to environments

it would be a good improvement if there was a way to add it to the game without killing people with bad computer's shit.

Or if there was an option to not have it visible on minimum graphics.

This is actually a really good idea, I can imagine mods where certain number of objects are visible on different graphics settings.