The dosdude1 patchers work better than I had expected. I have used them to install unsupported OSes on 2009 and 2010 MacBook Pros, and when you combine them with an SSD upgrade they are shockingly usable, and nearly indistinguishable from a modern Mac in terms of functionality (if not speed).
It should also be pointed out that you can keep using a machine for a long time even after it is no longer supported by the latest OS. What actually matters is when that machine stops getting security updates and new versions of things like Safari. So for the moment, High Sierra is still a very usable OS, but older ones are starting to run into issues.