I think a progen recustomizer would definitely be a good thing, as some people have mentioned. Personally, I'm happy with mine (except I messed up the under pattern on one, but I can fix that). But the option to change them would be nice for a lot of people, so even if I wouldn't personally use it, why not have it?
As for custom wolves: I think another option could be maybe it's something you earn in some way, like the wild wolf tokens we'll eventually get, but maybe more expensive (and still extremely limited). So something like it takes 10 wild wolf tokens or 100 of the token pieces, and still only 1-2 per year, or something. The other option I like is having them available to buy (again, in limited quantities) during the anniversary or some other special occasion. The tokens should be account-bound, naturally, and it might be most fair to have the wolves be temporarily entirely account bound (unable to be studded or traded). So you don't have to keep them forever if you don't want to.
I really like the idea of getting them from a special, once a year event. It both makes them more exclusive (can't get them year round), and inherently makes them limited. To be somewhat fair to people who can't be active, though, the event should last something like 2-4 weeks, so people have a chance to get in. The option of birthdays (or account anniversaries probably makes more sense) also seems good.
I hope that's coherent enough and not too rambly, I am tired.