There are efforts to make various components work in Firefox. The largest effort is "Stylo", which replaces Firefox's selector matching with ours. I'm not sure what the future is on Firefox using Webrender or our layout; though I suspect it depends on how well stylo works.
The plan seems to be to let Servo continue to evolve as a testbed for new ideas (like webrender), and share components with firefox whenever ready. An independent Servo product is not likely in the near future, since there's a lot of work to make it fully web compat. In the far future ... well, we can't tell :)
Admittedly, android-specific efforts have slowed down in the past few months, but I believe it is still a goal :)
I mean, Servo-as-a-product isn't even planned yet, and may never be, so by the time that question is relevant the ios rules may have changed, too :)