Oh no, I'm not falling for that one again. A long time ago a fledgling Opera browser also had an integrated mail client. I liked it enough that I started using it. A few years later Opera decided to stop development of the mail client and removed it from the browser, and since it was POP I had no way of moving all of those emails to a new client. The memory still rankles.

Vivaldi is a great browser and I say that with not an ounce of hyperbole. Stick with what you're clearly good at, don't ruin it by falling into the 'moar featurz' trap.