Who wants a canadian and inhumans arena with a four star selector rewards?

FaIIen

Need that sabretooth four star to do that carina challenge 0 for 25 in mutant-skill four star !!

Ercarret

Seeing how you can earn 3 and 4* champs from arena right now, you'll be able to earn him naturally eventually even if you don't pull him from one of the crystals. I see no reason why Kabam would cater specifically to Thronebreaker players who don't have the roster required for the challenges, when they don't do that to anyone else. While giving someone a 4* or two might not seem like a big deal in the grand scheme of things, it would in this one case allow you to get better rewards than I just got from becoming Thronebreaker and a lot better rewards than anyone who is not Thronebreaker yet could ever earn from a (basically) free champion. Even giving them a 6* Inhuman champion wouldn't allow them to earn as good of a reward as you can earn with those 4*s.

But as I said, just keep an eye on the arenas and every champion you want will become available to earn naturally.