Can you serve a multi-wire branch circuit off a pendant?
Can you serve a multi-wire branch circuit off a pendant?


YES


  What's wrong with this?


Sorry code cop.  Nothing

In the situation you describe, the pendant is also, not permanently installed equipment.  Code has no business looking further than that L14-20 outlet.

IMHO, it was an unnecessary expense to use the L14-20 outlet, and the corresponding plug, but its neither unsafe nor illegal.