I dont really think that situation would come up very often. I mean if you're doing console specific stuff (Nintendo virtual boy) than you're looking at something entirely different.
Arc the Lad is possibly another one.
Yeah, this is why I don't think the badges for "full sets" are a good idea. There are -way- too many platforms to consider.
Badges for collecting stuff in a series - not ALL releases, but a good chunk of it - is fine by me.
Personally, I like the idea of a 75% threshold. If the badges are about showing a user's loyalty, as forte said in his original post, then this would work very nicely. You can be loyal to a franchise without owning every single game. Hell, I'm a loyal fan of a lot of series and have a bunch for games for each, but I don't own them all. I consider myself a loyal Pokemon fan, even though I don't own Gold and Silver, the Ranger or Mystery Dungeon games. All I'm saying is if it's about showing which franchises we are loyal to, then a 75% threshold should be fine, that means if a series has 15 games in it, then that's 12 games you'd have to own to pop the badge, which is still a pretty decent investment into the series.
Now, we aren't going to be able to please everyone with whatever we decide to go with. But, we could still do 2 types of badges. A loyalty badge, and complete collections badges.
The loyalty badge would pop at 75% or greater, this could be automated fairly easily (I think). This would allow folks to look at a person's collection page and give them an almost "at-a-glance" idea of what that person's favorites are. So you could look at my collection and it would have something like a Castlevania, Grand Theft Auto, Pokemon, Metal Gear and possibly Resident Evil badges.
Then we could have complete collection badges for franchises, consoles etc. These would be mod awarded and require some kind of evidence that the person owns everything, counting spin-offs, ignoring variants, etc, for that franchise/console.
I also like the idea of publisher based fan badges. You can be a fan of a certain publisher without owning every game they've ever made. I'm a big fan of Konami because they make 3 of my favorite series, Castlevania, Metal Gear and Gradius. But I wouldn't go out and buy 15 million DDR games, just to prove how loyal I am to the company. So the 75% threshold and owning everything wouldn't work for companies, we'd need to come up with a different system for them.