This is what I hope to solve with the private addresses: These are not geo-marked and not routable. Eg. they are randomly generated and cannot be attributed to a geographic location (easily).
Ah nice! Glad to see you've already thought of this. Any sense of what % of addresses you would hope to be private vs geo-marked? (Asking because it's easy to mark all private addresses as being "bad" if they're in the minority, but once they reach a tipping point that becomes infeasible - at least we've seen this with addresses tagged as belonging to VPN providers).
If you have a decent amount of private addresses in the mix (1) such that blocking them would 'break' the mycoria experience(2) then it sounds like you've got a decent solution here - geo-aware prefixes for convenience and private addresses for when you'd prefer the anonymity.
1) I freely confess to not knowing what percentage a good mix would be. 20%? 5%? In practice, going back to the VPN example for IPv4, it's "a high enough percentage of important users complaining that their VPN connections are broken for a long enough time". Depending on the jurisdiction that can be 1% (well off / well connected people in a jurisdiction complaining to the right people that in turn overwhelm management with their complaints) to >20% (not necessarily well off or well connected users, but a critical mass that instead overwhelms ISP help desks with complaints).
2) Assumption: mycoria / the app you're building on top of it becomes so important that breaking it completely is a non-starter for the average ISP.
This is what I hope to solve with the private addresses: These are not geo-marked and not routable. Eg. they are randomly generated and cannot be attributed to a geographic location (easily).