You’ve used some phrasing that I am not really following. What exactly do you mean by “stable” in regards to an email address? And what is an “unknown” domain?
I do this for every website, not just financials. As long as you have a quick and easy way to create the email aliases and you’re using a password manager I think it can be an easy and effective boost to security.
This looks like an attempt to reproduce the web-of-trust functions provided by Keybase.io. Keybase has historically been a great resource that fills the same role as the PGP/GnuPG web of trust for a much broader range of identity attestations.
An open implementation of this concept has been sorely needed since Keybase got bought and shitcanned by Zoom during the COVID lockdown. Zoom wanted to aqui-hire all the Keybase devs to boost development on their lacking encryption and security. Sadly, Keybase has basically been abandonware since then.