Would it matter then, necessarilly, if they were actually IN the movie then?
For instance, if the "Build-A-Weirdo" concept were to take flight...
You could get basically a wave where the weirdo is just some Tibrian guy in a pretty "average" Cantina outfit. He'd have the same basic BAD parts (head/gun, 2 arms, 2 legs, torso). The kicker would be that the next BAW figure in the next wave would be, lets say a Duros guy (Bannis Keeg or just random). Hands would be swappable, head swappable (if it's like the BAD's, the neck could plug in, so random alien necks/colors wouldn't be an issue so long as he wasn't wearing a "V-neck" I guess).
I like the weird alien background guys a lot... I think that's a cool idea. It could work to deliver film and EU characters (Bannis Keeg seems like a pretty good example actually) and if it was kept fairly generic in the figure's design you could take the hands/head from the hypothetical Tibrian in wave A and mix them with the hypothetical Duros in Wave B... Likewise you could take a torso like Bom Vimdin's and swap arms that would make a unique looking alien wearing a similar vest...
I think the mix/match potential is better on figures/characters like this than it is on the droids. Some of the droid parts mixed around ok, others not so much.
The Trooper idea is less for the concept of building new, and more for simple value, honestly. Just thinking about the line today and cost, compared to the line not too long ago, and what you got, plus a lower cost. Like I said, the Gammorrean Guard's nice, but how many of those has Vintage delivered at the inflated prices?
Anyway it's just fun to speculate... Vintage will end eventually, and I totally do not expect Hasbro to give a pack-in to collectors with significant umph to it like BAD had. Just like thinking about what would be neat if it did happen.