My personal opinion; but it seems the minimum spec in terms of
connections is labeling. My point is that you can use whatever
connectors your like on the outputs and label them appropriately
and you'll be no worse off than a regular consumer AV receiver.
I think a variety of speakons still leaves room for incorrect
connections, but I haven't studied if some collection would
accomplish your one goal.
The only sure-fire way to prevent incorrect connections are a variety
of connectors, like 1/4" phone for one, speakon for another, and
banana for the other. Can't mix those up, and all are certainly
viable for speaker connectors.