Accessory packs are a cool idea and I think there's a good chance they'll do SOMETHING along those lines in the next few years (even if just as a Hasbro Pulse test run). Basically I would not be at all surprised to see something along the lines of the Transformers exclusives they've had: A figure (probably a troop builder) packed with a TON of accessories that aren't necessarily related to that figure.
Accessory packs have some challenges though. All of your ideas are fine, but not every Marvel Legends collector is a completist. So now you have to consider how you market them. A "Catch all" that's got a little bit of everything risks turning off those that only collect particular segments. Do you mix comic-based and MCU-based accessories in the same pack(s) (and sure, there are plenty that could be both, like Spidey Web FX and such)? Not saying it's insurmountable at all, but it's not simply as easy as "put out a big box of stuff!"
I suspect the first thing we're likely to get is an "FX Box" that's got all kinds of energy-blasty things (both old and some new) and probably the same stand that came with the White Widow. Basically something pretty generic that can work with a lot of characters. After that maybe a weapons pack with a giant pile of nerf guns (and maybe a few realistic ones) complete with "pew pew" and smoking barrel FX and the like. And after that you start getting into "team oriented" packs that have say, one set that's a bunch of Web FX and stuff that works specifically with certain Spider-Villains (and maybe some appropriate alt-heads for a couple characters), and another that's got optic blasts and slashy-claws and TP/TK FX for the X-Men, etc...
But who knows? Like I said, I'm pretty sure we'll see them attempt SOMETHING in the next couple or few years, though whether it ends up being something that basically disappoints everyone or that is wildly successful remains to be seen.
EDIT: I wonder how feasible it would be to pack in some of the "Civilian" figures that were discussed briefly at Fan Fest with a bunch of accessories. For example Jarvis with an "Avengers Accessory Pack" and maybe Aunt May with a Spider-Man Pack, or Alicia Masters with an FF pack, etc....?