Would be kinda hard to balance... and they would probably need an average power of 7 or more to be of any threat (if they can't even get past the high attack manip clans, they'll be too risky to play). Then comes the damage issue - surely allowing them to 2HKO would be silly, but if they are going to be a pill manip clan operating similar to how some of the older piranhas act, then there's always the issue of how well they operate compared to dahlia Scubb Hawkins etc.
It's quite workable, IMO. The scariest pill manip cards either have SoB (Piranas) or a round winning bonus (Shann, Tremorh, etc.) As these guys would need to pill up a little harder to overcome attack manip clans, that +2 pills bonus wouldn't be nearly as scary as it initially seems. Most attack manip clans already offer a 2-pill benefit against a 7 power with no round-winning bonus.
Moreover, like the Vortex, they could make up a strong pill-related bonus with shaky base stats. Vortex abilities help make up for those, but they suffer greatly vs SoA... So you could expect to see something like a 3* with 7/2 +3 Life, and it would compare well to existing cards. They might also have a couple of cards with good all-around stats, but with interesting Backlash abilities. I can imagine a 5* with 8/7 stats but a Backlash of Poison 1 min 1... Comparable to Selma in many situations, sometimes a bit better, sometimes a bit worse.
A major difference between attack manip and +pills is that attack manip forces your opponent to either spend pills or take a hit, and therefore encourages moderate pilling, since you gain a life advantage if you win or a pill advantage if you lose. +pills only works if you win the round, which encourages overpilling and turning games into mindless 50-50s, even if the +pill card is theoretically "balanced".
For example, look at how people use rowdy, compared to how they use Scubb (even though Scubb is the more balanced of the two)
@Subclavian: I think you're exaggerating the impact of +pill cards a bit. Like I said, cards like Scubb don't really compare to this clan idea... Scubb has SoB, which means he is better at beating Rescue and Montana than a 7 power.... And he gains 4 pills instead of 2. I don't see a hand full of +2 pill cards creating a 50/50 situation, personally.
Another way of looking at a clan with a +2 pill bonus is: they will get less extra pills in a typical game than a Vortex deck. Most ELO players consider mono Vortex pretty much unplayable.