Externally, Firefox has become a brand. Servo is comparable to Gecko or WebKit (it is a browser engine), although it is new, not finished, and uses novel techniques.
What follows is speculation on my part. I am not a Mozilla employee.
Mozilla might, in about five years, offer a new product for desktops which features Servo, SpiderMonkey (the JS engine currently used in Firefox), and an as-of-yet undefined chrome (the UI bits around the rendered page). It may be a mobile product instead, or a product for a different type of hardware, although the current thinking seems to be to target it for desktops.
Whatever that product is, it may still be called Firefox or a derivation of that brand (as Firefox OS was), although it might have a completely new name (it worked for Microsoft Edge, after all).
Since some of us in this thread work for Mozilla and on Rust/Servo, I would like to point out that this number is your own speculation and nothing official, timeline wise. Nothing the matter with that! Just don't want people to get confused.
What follows is speculation on my part. I am not a Mozilla employee.
Mozilla might, in about five years, offer a new product for desktops which features Servo, SpiderMonkey (the JS engine currently used in Firefox), and an as-of-yet undefined chrome (the UI bits around the rendered page). It may be a mobile product instead, or a product for a different type of hardware, although the current thinking seems to be to target it for desktops.
Whatever that product is, it may still be called Firefox or a derivation of that brand (as Firefox OS was), although it might have a completely new name (it worked for Microsoft Edge, after all).
(Updated for clarity.)