You make the problem sound like it's lack of IPv4 address space.

That is true in some respects because the method of allocation of these addresses is not straightforward and has its own set of problems.

But in actuality "the problem" the OP is encountering is that for the RTC developer/user, a publicly reachable IPv4 address block is too expensive.

With a publicly reachable IP address (most ISP's will provide one, often for an additional fee), you can do peer-to-peer quite easily.

UDP hole punching works fine, save for when both peers are behind the same NAT, in which case you need a peer outside the NAT to forward traffic.

And it's easy to simulate a LAN over the internet using encapsulation.

Gamers have been successfully hole punching for many years.

I'd say up until recently, gamers have really been the only group that has demanded peer-to-peer connectivity and made it work.

One wonders if every ISP customer were willing to pay the extra fees (if any) and requested a publicly reachable IP address, could the ISP's meet the demand?