@polotek That's a good point. At least one of the two frameworks does need to be updated to something with better LTS. We actually enlisted an org that does LTS support for hire, so we can take our time on updating things instead of stopping to do an emergency refactor with a months-long opportunity cost.
There was a "just rebuild it now!" push for a bit but it wound up exactly like it always does, dragging on in a quest for the "perfect" design, reintroducing regressions, etc.