While I agree that having more than one SMB may be the way to go, part of the reason for purchasing these "big ones" was the multifunction aspect, it's an SMB, a Saftey Stop Anchor, and a liftbag all in one; in short a multi-tasker. My feeling is that the more gear on your kit that has more than one function, the better, in this way your saving weight and bulk since items will have more than one use.
Splitlip- very interesting idea, I assume that by using surgical tubing, the "plan" with this rig setup would be to tug on the spool line attached to the SMB that's tucked under the tubing, thus "reeling in" the smb when you need it. I'm just not sure that the tubing would hold the SMB in place during entry/exit, for example, giant stride entry or backroll entry, I can envision the smb slipping out from the tubing in such a case.
I'm going to invistigate the "attach to the bottom of the backplate" idea's right now. Be back in a little bit.