9 speed for MTB's is becoming relegated to lowed end components, wouldn't worry about availability of chains or cassettes for may years, but 9 speed XTR shifters are long gone, with XT sure to follow soon.

Not seeing the issue of 'planned obsolescence' MTB components, if used only last a few years, and the cost of replacing with the current spec parts will be the same as if you had to search for NOS parts.

MTB's have stuck with legacy parts for so long now, that change is hard to accept, we still have 135mm OLD rear wheels, 9mm QR's on the front, 1 1/8 inch headsets, 27.2mm seatposts etc, none of which are really suitable for modern riding.