For me, a lot of the appeal of Smash Brothers comes from its awesome roster of Nintendo characters, most of whom have never interacted with eachother before.
So personally, I have zero interest in Brawlout. At this point. Because they very well realize what's needed to increase interest: guest characters. In fact, personally I think they shouldn't have bothered with original characters in the first place (except for maybe one and/or the boss character), and that they should have filled the game with other indie characters.
The drifter is a cool start (I don't know Guacamele), imagine if the roster would include Shovel Knight, Shantae, Yooka & Laylee and other famous indie characters (just name your favourite). They could beat Nintendo to the punch with some of them. I'd buy that game. And since new indie hits will pop up every year, they could things fresh if they make a sequel every few years. Smash Bros' roster will largely stay the same, but this has the potential to have some wildly varying sequels.