Not really a first priority thing, at all, there are much better ideas out there related to actual gameplay and features. Those are just pure vanity/cosmetic suggestions (which may still generate some stable income for Cyanide)
First of all, in-game Shop's UI is horrible atm. You can't say at a quick glance which one skin is for which one team by looking at its name in the list, you need to select it to see a picture/read its description. You need to surf through all the pages for skins for team you are interested in. There must be a set of filters, which allows you in 1-2 clicks limit scope of displayed items to, say, just Orc team's items; in case of future addition of items of other types (see below), there should be additional filter button limiting scope to specific kind of item. Such half-hearted approach won't sell you much stuff
I've just also thought about 2 new types of pure cosmetic/vanity items to sell:
"Passive" custom animation items. That's basically any animation following some in-game action - like movement, block, dodge etc, - which are played every time the action happens. To be a viable option, something more flashy/funny than defaults should be provided, preferably in a bunch of variations (value of an item diminishes if it's used by everybody around, so enough variations of each animation are needed for them to see some demand). Like funny goblin walks, spectacular elven passes, ferocious Mino blitzes animations etc. Some reasonable priorities could be assigned, still, like more accent to power play's animations for orcs and dwarves, but no custom Leap and Pass animations for them, as they won't be used that often at all, etc.
Taunts. This is a totally new cosmetic feature. If assigned to any of your players, it can be activated any time this player starts or ends his action (if he is standing at this moment) and results in a quick funny/flashy/provoking/celebrating animation visible to your opponent as well, which can't be skipped; it also should forcibly use the "slow-mo close-up scene" camera mode used by default for blocks and touchdowns, ignoring client's settings for such kind of scenes ("slow-mo" aspect perhaps could be dropped here). To prevent its abuse, usage of this feature should be limited to 1-2 times per half (regardless of number of Taunts assigned to players). It also must be made short enough to not produce too much anger from players which prefer to not use Taunts, or disable "close-up slow-mo" scenes at all in camera settings.
In case you own several animations for some specific action, you should be allowed to individually assign them to each your player (not just to all linemen, but to each lineman as well). Something like "animation slots" should be introduced for this. So you could give one custom animation to 3 your regular blitzers, and another very special one to your 4th blitzer star, to make him stand out.
For each type of animation (Dodge, Block, Pass etc) it should be allowed to employ several possible animation items for each player, randomly selecting between them, thus adding more variety to visuals. Yet, stacking too much of such shouldn't be allowed, as it will lead to behavior of assigning all possible animations for an action at once, thus limiting customizations options (as all teams with them will have the same set). Should be limited to 2 additional items max, thus resulting in 3 Pass/Dodge/Block/etc animations in total (including the default one).
One very important thing to emphasize here: it must be done in such way that all those customizations are visible to the opposition, even if the other coach didn't buy them himself. Otherwise its value will significantly drop in eyes of potential buyers It's not a joke: in fact, not so many people will be ready to pay for cosmetics which only are visible locally. Though what I propose above are mainly new animations (thus additional space required on disk), I don't think it will be a big problem. As far as my understanding goes, models and animations data can be distributed separately, and the latter is relatively light-weighted. So making it a part of every BB2 client, so they could be played for any coach, if used by the opposition, shouldn't increase its size for too much.