The Gemini app has been backported to at least Android 14 as far as I could tell (that's the oldest OS I saw it on), probably further.

Hard to say they're going to keep giving you new features, but buying a device for the future things that may be brought to it is always a massive gamble, like buying a Macbook for their failed promise of Apple Intelligence or a Windows laptop for the promised advantages of Copilot.

If the device works well enough to be worth the money, it'll keep working. If you want fancy stuff in the future, hold off on buying new hardware and wait until the stuff you want is actually available.