I think you're splitting hairs. If you're setting a safe speed to ride, just like any other conveyance, you either adhere or you don't, but putting additional regulations in to somehow curb the equipment just seems draconian, illogical. At least to a point. And yeah, at some level of motorization the bike ceases to be a bike, whether to be allow at all or not.
If no one is patrolling the freeway I can go 100mph in my car. [shrug] If they are I'm likely to get cited.
You're talking about a limit and enforcement like they are inextricably connected, and they're not. If limits are set and not followed then enforcement becomes necessary. Otherwise people self-police. Wherever there are rules and limits there may or many not be an enforcement element present. Does that mean you shouldn't set them anyway?
I don't know why this seems complicated to some. Must be a different mindset. I'm just not getting it.
Waterways are a another example. For inland ways they're set for safety, but even more importantly to keep wakes down so as not to upset moored watercraft. This goes right along with your paved bike path example - the limit is set for the safety of others present - which my example again was, you couldn't make 28mph on that strand if you wanted to. The speed limit is set for 10mph. If you're exceeding that, regardless of the conveyance, it's a violation.
Oh well, I'm out. Have fun with it!