I guess I have an unpopular take for you, too:

* We have a Cambrian explosion of clients right now

* Switching clients essentially friction-less

* Users are aware of which client is open source and which not and prefer the former

* Most clients are one-man shows but some are incredibly productive, churning out features like there was no tomorrow

* We promote and celebrate the openness (open source, standards that allow to switch client), so any premium features exclusive to your client will not be appreciated for long.

If you have anti-features and your product is open source, people will use the fork that doesn't have those.

The marginal cost of users is zero for the client, so charging for use is hard.

For relays though the marginal cost of users is not zero and whenever something is not free, it's easier to have a profit margin.

* You could have your client set a default relay and charge for its use past some basic onboarding use.

* Relay operators will pay for referrals. As operator of a popular instance, that could turn into a stream of income without having to maintain your own relay.