IPv6, needed for modern Internet not to collapse, would make many other important things easier. Easier to become an ISP, to selfhost, to build P2P networks, etc.
I really hope matrix gets native VoIP. I saw like 2 years ago it was in beta, haven't kept up with it though. I'd also really like voice channels like discord so my friends and I can replace discord but it seems like matrix isn't interested in being a discord replacement
Matrix I have doubts about. The idea of Tox was nicer, but the implementation quality and the scandal at some point didn't help.
Tox felt more playable, like piping files over it or a remote shell over it (I know, bad associations, but still), or even using it for VPN. I think there were clients allowing to do such stuff, and the protocol allows it.
EDIT: I mean, it's still alive, just don't see it claiming the place of FOSS old Skype replacement as it did.
GNUNet - all you people mentioning it have peers? I tried to set it up a few weeks ago, couldn't get peers.
to be clear, I2P is not really intended for anything, it's used for everything. It supports all kinds of things, and there are people doing all kinds of things on it. Though i could see potential technological limitations being a problem.
About Tox, I am not a fan of mixing up universal delivering of packets and applications. Piping files or using as VPS feels like something that would be better done with proper full network and not be mixed with chat.
There are no IPv4 addresses left. So you eather go IPv6-only, which would make many services not work. Or wait in a long queue to repurpose address spaces marked as depracated which would soon run out too. And then you put clients behind double or triple NAT doing having shitty service.
A lot of orgs (mine included) are sitting on large chunks of IPs they don't need (we have a /16 and several /24s) because they adopted early, got an ASN and prefix assigned by ARIN, and their addressing scheme is now so disjointed and scattered that they can't sell off anything bigger than a /22, and that makes setting up BGP a pain. Juice ain't worth the squeeze.