There is no reason why clearnet single hop relaying wouldn't be possible as well, the relays simply unwrap their layers and forward them to where the revealed message says to go.

It's been part of the plan from the beginning of the idea - the initial idea came from the idea of running an indra server on a wifi hotspot router, so that anyone can come along with an indra client, connect to the router, make a payment through their lightning channels to the Indra seed nodes channels and then forwarded back to the router to establish a session and then the user's client simply can fire off more sats to the relay's lightning node and get online without any rigmerole or contract.

But on the other hand, even though the user is paying for it, it may be that the user is doing something underhand with their messages that are now appearing to come from the relay. So, fundamentally, the reasoning for why all such traffic needs to be routed through at least two intermediaries before reaching the target, to emerge either at a server being run alongside Indra by the relay (for distributed networks like Bitcoin, Lightning, Bittorrent, Nostr) or at extra charge, forwarding traffic out to the clearnet, either on any port or constrained to a limited set of types of traffic.

The ultimate goal is that Indra (and by extension, Bitcoin and Lightning) become standard components of an internet router, and there is no "outside". And then we just need an anonymous, decentralised DNS protocol, probably also built on top of Bitcoin and LN, that resolves network names rented by users paid for with LN, to their hidden service public keys, which can then establish connections with the help of introducers that intervene for the initial connection routing header and then can stand aside as after the first message is sent, the other side has a routing header, pops it inside its own 2 hop routing header, and voila.

It's a little bit like sending a self addressed stamped envelope to someone, enabling them to send you a reply, except that it's fully anonymous.