anyway after sleeping (badly) on it the NM by default plan makes sense. my remaining concerns are twofold

• "NixOS is declarative, right? I want to make my IP static (or whatever). let's search how to do that. hm, apparently it's networking.*" – now you're mixing NM and scripted networking
• when we switch to networkd by default, risks of potential conflicts between NM and networkd when people do want to declare parts of their networking config

for the former, we can probably solve that by useNetworkd by default + deprecation notices in the networking.* docs + gradually getting rid of stuff. I assume that if we're not relying on useDHCP any more then ElvishJerricco's qualms with the interface simplicity don't apply and we're okay with making people learn systemd.network.networks."40-foo" = { name = "enp1s0"; networkConfig.Address = "1.2.3.4/24"; ); rather than networking.interfaces.enp1s0.ipv4.addresses = [ { address = "1.2.3.4"; prefixLength = 24; } ];, which is both shorter and also will make it explicitly clear to people when they are mixing networkd and NM.

I haven't tried doing the latter myself but I guess it's probably a well-trodden enough path that it works fine as long as you're not explicitly configuring conflicting things?

works fine as long as you're not explicitly configuring conflicting things?

Exactly that.