I personally find mummy very interesting as an ability. A large amount of pokemon in the ou tier are given their high usage rankings in part due to their abilities. While most of these abilities might not be game-breaking, they still act to buff the pokemon. Mummy should be seen as a debuffing ability used to make other pokemon easier to deal with. Anyways, as I browse through the list of OU pokes, I can imagine many situations where mummy can give your team an advantage. Sometimes that advantage can be very significant (auto-winning weather wars against Ttar, hippo, and physical abomasnow). Other times, mummy can just serve to weaken the opponent's team by getting rid of abilities like technician or poison heal. The rest of the time, mummy will have practically no effect on the opposing pokemon.
Mummy itself does not create much risk. The only risks to using mummy are getting rid of nerfing abilities like truant or spreading mummy to your own team, which in some cases can be a pain but mostly is not a problem. Aside from that, if the cap were played as if it had no ability, then the player could only benefit. It is the player that will use mummy to create the risk. Mummy can be used aggressively in an attempt to actively debuff the opponent's team at the risk of the CAP's health. If we use the sweeper stat spread implied by the primary ability, the CAP may not have too many opportunities to debuff the opponent's team, especially with hazards up. The player will sometimes need to decide if the removal of an ability like moxie, sandstream, or regenerator is worth losing a member of the team, a member that may have had other responsibilities. The temptation of a great reward will result in riskier play and result in either great benefits or a squished bug.
I believe mummy is a great fit for this concept and can work quite well with weak armour, although I'm getting pretty tired so I don't feel up to writing an explanation at the moment. As for the other abilities, I believe all the self damaging ones are really boring. As the soldier worm said before, I would rather have an interesting failure than a boring success and I feel that all of the self damaging abilities are far too limiting and focused. But hey, if it rocks your socks...