Belated thanks! Sorry, I forgot to reply sooner.
I did some quick proof of concept testing with the coupling plates and Technic axle pin. I should have made some notes or taken photos but from memory it seemed like a good solution using legal techniques which I'd like to explore further and document this time around.
Initially I set out to make a length of track that was 32 modules long (when straight) that could be used for a 90º curve or flexible track, but found that there was some asymmetry along the length in where the pivot points were located. I think it was possible to correct this but it requires one segment of the track to be slightly longer or shorter than the others.
I wondered if you had any thoughts on an ideal curve radius for a monorail setup, taking space and functional stability into account. Would the original monorail or the train track be a good place to start?
I've since taken delivery of a load of rollercoaster track so I'll hopefully have a (not)monorail system to share in the future. Now I need to look into Power Functions/Powered Up.