Android should take a similar path. Mainline the kernel drivers, keep the minimum system requirements low (which you'll want to do anyway for 3rd world handsets), add developer modes to test apps with constrained RAM and throttled CPU, rank "eco-friendly" apps that have lower storage requirements higher on the play store.
As far as the human resources required, see Ubuntu or Redhat Enterprise, which manage to do ten year support cycles for servers. I think handsets could be easier if you keep upgrading the kernel and core components instead of only applying security updates to the existing software. If you can do that then there's no more security work than you would otherwise be doing, since your latest handsets would need those security updates too.