You are right; it's a bit of a excuse. Tons of small services under Unix (by default) listen on several interfaces and networks. I think Bitlbee itself listened on 0.0.0.0 instead of localhost. Ditto with some UPNP/DLNA daemons.

It takes very little to set up IPFS to just listen to tun0, disable routing (let ygg do its job) and throttle the bw a little so it doesn't hog the whole network.

I would be surprised if the Kubo/IPFS developers didn't already configure Ygg for themselves, as both are software written in Go.

The author of NNCP https://nncp.mirrors.quux.org/ (and the other author from Tofuproxy) are pretty much aware of Yggdrasil.