Non official chains suffer from the fact that few if any miners are going to mine them so they lack security on par with the main chain. And more over most users aren't going to use them because its not magic.

That being said think they are and will always be a great place to develop and prove out concepts.

If my ultimate goal is official side chains that include part of the reward such security is at parity between all chains and that the official software automatically enable users to distribute their burden, would my course of action be to build an external proof-of-concept side chain of side chains?

or do you doubt that official reward splitting chains will ever find their way into bitcoin core?