The example that you give as what could be considered an approvable ability speaks volumes to me about why powers and abilities are not approvable.
The Geass ability is used by several characters, each being different to each user depending on personality.
So this ability affects each character differently - which means that the ability itself is not what you are a fan of, but how the individual character utilizes that ability. Therefore, the ability is covered under each character's fanlisting.
An unapprovable ability is the ability of becoming a Super Saiyan (in Dragonball Z) since this ability is held by the Saiyan race. Although significant, it's restricted to a specific race and specific races are not approvable (I assume) and saying you are a fan of super saiyans means you are a fan of that race
If a power is held by an entire race, then it is a part of the racial characteristics. While specific races are not approvable, once again, any individual character who is approved and who is of the specific race will also be a user of the power is question, no? So then that power would be part of what makes you a fan of the character.
Suppose with applying for an ability or power, the person applying must provide examples so the concept is not misused.
That's the thing - powers and abilities are
concepts. There is nothing tangible there, there is nothing that you can truly point out as being what makes the concept specific and concrete. It isn't like an item, or location, which is there and tangible. With a power or ability, it is either something you are born with (part of the character) or something that you learn or aquire (becoming part of the character). Approving a power is no different than say, approving the ability to ride a bike, or the ability to solve REALLLY HARD mathematical equations. Both could have a meaningful impact on a character or series, but it isn't something that can be defined by a set... uh, definition.
I think that the enjoyment of a power or ability is the enjoyment of the character or series as a whole (I mean - do you know anyone who likes the Geass ability but hates the series?) and as such does not need to be approvable.