Not only for /e but linux roms in general. I want to get a pixel 3 which is barely supported right now (only extended supports) and i don’t know if some features will still be well available whether it’s related to push notifications and app installations once it gets no longer supported.
I can’t say for eOS (others may) but for Linux-roms you may check in at the specific forums and websites to find out about the current (and future) working/supported features of that specific device.
Are you referring to Android Custom ROMs such as /e/OS, LineageOS etc. (as Android OSes use a Linux kernel), or are you referring to Linux OSes on smartphones such as Ubuntu Touch, postmarketOS etc.?
i am referring to custom roms only