What are some ideas you have floating around that you don't have any plans on writing but like to entertain as a thought?

Many of them, in fact! Though they sort of vanish from my memory if I don't make a record of them, here's a few ones I jotted down when they came to mind.

For a domestic one: Bill thought he'd hate a lot of being married! Even though he loves Dipper, he thought he'd rebel against the chains of domesticity - and in some ways he still does - but one major benefit he's found is not having to be 'on' all the time.

No need to be perfectly performing all the time! No shoving around for social influence, no intimidation, or clever tricks. No commanding attention or taking up the room. Hell, there's surprisingly little upkeep! Bill can undo his tie and pick his nose and bitch about his day to someone who isn't bending over backwards to agree with him on everything. Someone who doesn't give him a weird look and sneer if he, god forbid, actually wants to sit down, read a book, drop the grin for an hour or two.

The concept in question is Bill's very first moment of great surprise. That when he isn't being the most charming, terrifying, and exciting guy in the universe, and just chilling out for like, five minutes, Dipper comes over and snuggles up to him on the couch, or wraps his arms around his shoulders and kisses the top of his head. And when Bill asks 'what was that for?', Dipper shrugs and goes 'eh, just felt like it'. It's both baffling and extremely compelling.

A short where Reincarnated Dip is Definitely Sure he's Not Gay!!! Especially not for this Hot Demon Man who is getting so close and touchy with him with his big smile and horrible wiles. Yep. Just keeping an eye on him to make sure he's not up to something Nefarious ™.

A discussion between Dipper and Bill where Dipper insists that Bill should understand this, or not do that, because, like. Y'know, Bill's a guy! There are guy things! Making Bill stare at Dipper like he's an idiot. He proceeds to informs Dipper how that's stupid for multiple reasons! First, that Bill's Not Human to begin with, his gender can't be put into a little box! And frankly, he never filled out the paperwork for his original one, come to think of it. Sure, he/him's fine, but c'mon, sapling, thinking of the whole shebang like a binary is dumb as hell. Now Dipper has to do some mental readjustment re: his own issues with masculinity/gender.