GFCIs don't work on multiwire circuits because of the shared neutral ... how about AFCIs? Anybody tried? I've learned things the hard way too many times. Figured I'd ask before screwing up.

Same as GFCIs...you can get expensive 2 pole ones that work on mulitwire circuits.
Don

Just to cklarify, you can use a multi-wire circuit with GFCI protection as long as you split the neutral where the GFCI's are fed.

That is, by using receptacles, not breakers (unless they're breakers in a sub-panel, in which case, the 'multi-wire circuit' is actually a feeder.)

In other words, the 'load' terminals must have separated neutrals; they can share a single neutral at the 'line' terminals.

I've done this where a jetted bathtub required two GFCI receptacles, for motor(s) and heater. I ran a 12-3 rather than two 12-2's.