Yes. Inviting someone to Nostr should come with some way to be notified if they accepted the invite, so you can immediately follow them, bootstrapping them into your web-of-trust. I believe ManiMe (nprofile…9wgx) is working on something like that with https://nostrmeet.me/
Another thing clients could do is default to adding a certain amount of PoW to new users' notes, defining new users as those with no kind 10002 relay list, or no notes on their outbox relays with a timestamp older than X number of days. The exact number of days someone should be considered new is debatable and each client could use a different length of time. Then, clients could default to showing notes from npubs outside of the user's WoT that meet the minimum PoW. Coracle has the latter option, for instance, but no default PoW added to notes for new users.
The above could even be paired with a feature like Nostur has, where you have a few seconds to cancel a post before it is written to your relays. That way if you see a typo, you can cancel and fix it before it is permanently on display. During that few seconds, the client could be performing the required PoW.
The first idea probably hinges on DMs working consistently for the notification when someone signs up that you invited, and DMs are quite a mess right now.
The second idea hinges upon more clients supporting PoW. The only one I know I can add PoW with right now is Coracle, but it's off by default.
I am also interested in hearing any ideas you might have about bringing the incentives of paid relays into alignment with participating in the guardianship of the network overall. You had mentioned that the way Bittorrent accomplished this was an example to follow, but I am not terribly familiar with the incentive structure there.