I'm not sure Start would be viable, at least if quick weapon switching is to be available for multiplayer. I overloaded Start with safe save state because I figure a pause primarily meant for save states made sense as a single player feature, and because Start is often a pause button (SoM's got pretty atypical button assignments), so having it be a button combination (like in zhaDe's original set up for NGI) was overkill.
A combination press for quick weapon switch isn't unthinkable, it just isn't super trivial to implement. Changing any of zhaDe's hotkey code usually involves untangling side effects, not because there's anything wrong with it, but because there are so few buttons, they're all already used for something, or often multiple things at this point. For example, the reason R + X is non-trivial is if Manual Blocking is on and overrides R, when you press R it triggers the block animation, and weapon swapping needs the character to not be playing a block animation (among other things, keeping the explanation plain). So you can make R + X not block (or stop blocking), but it takes time for the character to stop blocking, so you'd have to hold R + X to get a weapon swap... but then weapon swap code would need to be changed to wait until a swap is okay rather than seeing the buttons, knowing now isn't a good time, then not recognizing that same press until they've been released (I actually already did change this button logic in a previous release to make it more tolerant in combat). Weapon swap would work with a perfectly synchronous press of R + X, but strict timing for something like that would suck. Setting the hotkey to R + X (or whatever button or combination) isn't the difficult part; having the buttons not conflict with others is. R + Start has similar considerations on block animation timing (the inverse of your suggestion), plus if you release R before Start, avoiding triggering any of Start's other behavior.
I get that you want vanilla X behavior back, I just haven't found anything adequate for an alternate button choice.