For a really wacky idea, what if Vin's sister was an Allomancer (seeker maybe, if we go with the power-stealing idea)? We know her blood line is really strong, so maybe there is a higher chance with her family. Is there any proof that Reen was as well? That could explain how the inquisitors finally caught up with him. Maybe when they 'killed' Reen they used him to make a new inquisitor (like Marsh).
This is what I was originally trying to get at. For the power stealing to work, the sacrifice would have to have allomantic abilities (and 1 would have feruchemy). Thus, vin's sister would have to be a seeker, which is not likely (unless it's through the same mom...I don't know). Reen likely would not be an allomancer as he was only her half-brother.
Darxbane, for the reasons you mentioned, I was thinking that any additional powers an inquisitor had would have to be useless in battle. Like, you don't sooth someones emotions in battle. So abilities of this general nature would be what we were looking for. Not necessarily useful in battle, but elsewhere maybe.
Chaos, from now on I will be attempting to use the word Hemalurgify in all my posts on this thread. That's got to be the coolest word ever.
I honestly don't know what the big deal is about the difficult to replace quote. If your going to stick eleven spikes in someone placed just correctly to give them special abilities and not kill them in the process (even though all logic says they should be dead), I would classify that as being difficult. No need to complicate this any more than that, according to Phaz's razor thingy (which I'm to lazy to find and actually use...).
The Inquisitor allomancer theory has its positive and negative points, as does mine, but I'll be honest, I just don't like it. I don't know why, it just seems too easy to me. Which is kind of funny considering that in the previous paragraph I mentioned keeping things simple.
I've always envisioned hemalurgy as a third full system with unique abilities. If it is just a process to gain allomancy, I'll feel somewhat cheated.
Thanks for posting though, I really like some of the ideas going around.