djdelorie, the error idea is good, and it's the missing half of this. With a radius reference available, the state space for a rotary cutting move in G94 becomes:
G93 active: fine, inverse time.
G94 with a radius set (INI default or a G-code word): fine, surface feed.
G94 with no radius anywhere: today this silently runs deg/min, your "stupidly slow" case.
An opt-in INI guard makes state 3 a hard error instead of a slow wreck: "rotary feed move with no radius reference, add G93 or set a feed radius". Loud failure with the fix in the message, instead of finding out by watching the machine crawl. Every rotary machine then either runs a correct feed or refuses to run.
The guard alone is worth having even without the rest, since it catches the forgotten-G93 case you described, which the feed feature by itself doesn't. Cheap to implement, breaks nothing, machine builder opts in.
On "anything new is work and learning": agreed, which is why I'd keep the operator-facing part to one G-code word and let everything else default to today's behavior. The guard is the one piece aimed at operators, and its whole job is to say "stop, your program is missing something" instead of teaching them a new mode.
