My philosophy for the KISS is that for the diving I do with it (open water, 80m ish max) I can easily carry enough OC gas to get me out without being bent stupid. Even more so if you include buddy's gas and deco station gas, and if I've had a RB problem and lost my deco gas and missed both of those I just hope the pot fixes me up enough that I can start playing golf

.
So adding extra complexities like pluggable off board gas seems to go against the KISS principal. Naturally YMMV!
It's all down to failure analysis - what problem are you trying to fix, and are you fixing a symptom or a cause? From your DIR days an analogy would be someone carrying a pony in case they run out of gas...
just my .02c
Keith