Super cool. Excited to follow along!

As a data point (probably closer to anecdote), I'd be willing to pay for just an email client. I don't know about recurring payments yet, but something like Superhuman-but-cheaper is definitely something I'd consider. My only real option right now is Outlook, I think.

Why anonymous? You are after all asking strangers to run your code.

Have you considered going the donations / sponsorship (e.g. patreon) route. This seems like it leads to much more sustainable open source projects than VC money which often leads to a project flaming out when the investors come to collect (or the company gets acquired).