How good are your programming skills?
You say you want your Edge to remain relevant, maybe you mean as flashy as possible. Both the EE and PE will remain relevant for what they were designed to do as ling as they keep running. Yes, they are restricted in what they do and what apps they can run and those restrictions were built in at the design stage.
If you want to run the latest and, maybe, greatest apps you will need to either change much of the hardware inside the Edge or rewrite the release of Android you want to use so that it will work with the hardware we have. That means adjusting the APIs and even the kernel to work with the rather ancient processor in our devices. Then there is the somewhat restricted video subsystem, audio should be OK.
Having got all that working there is the the integration of the e-ink side of things that will mess with what you have working so you start again.
How do I know this? I asked the programmer I employ if it was feasible, she asked several of her friends in the programming world and the answer was maybe, how much did I want to pay for several months work of several programmers knowing that there might not be a good result at the end.
The idea of a complete rewrite of the latest Android to allow it to run on my EE has now been shelved as far as I am concerned unless we suddenly get a windfall of a very large amount of cash in which case I would consider reviving the project - there are several things I would like to improve and fix on my EE, like more integration of apps with the e-ink screen, the ability to run firefox with its plugins, the camera working again and so on.
Beyond that there is the possibility that a rewrite could be undertaken by a number of programmers working in their own time from the goodness of their hearts to help us BUT something like that would take a very long time and still might not work.
I know this is a rather long answer to your question but you are not the only person asking.