...we need more rendering engines to prevent a monoculture.
Indeed. But that might not be the thing that is all decisive. The world changed since the Netscape days...
Gmail struggled a bit, as Google insisted "this browser or app may not be secure" on some attempts, but loaded the email client on others. Similarly, Google Maps was also a little unhappy; fine showing satellite and Street View imagery, but less so with displaying an actual map. Web versions of Microsoft Office also struggled to load and Netflix simply ignored the entered password.
In today's world others will decide what is the best browser for you. So that you don't hurt yourself. And thus the most likely course of history will be that this either dies, or is bought and integrated into an "acceptable business proposition".
Biting the hand that feeds IT
