Doc Chaos is totally right. As long as it does not interfere with the GMs Adventure
(Troll streetpunk in an Tir Taingire Elvencourt High Society Spy Adventure) we should play whatever we want !
No problem, who stands in your way ? talk about it with your GM.
Now, Catalyst gives a ruleset supposed to fit with the basic-classic background and style of gaming, including frequency of metavariants in their BP cost, I think that's a good job, but they never said you had to respect it.
You want free metavariants, or characters build with 1000 BP ? okay, why not ? that's just not the basic-classic game.
Which basically noone cares about. We are the players. The heroes. We want to play the cool stuff!
Oh, yeah, but you know, old rule, if everybody's cool, then nobody's cool.
I find it better if metavariants stay rare, or the game quickly turns into a ridiculous freakshow. But "if that's what you're into…"