This (maybe) addresses the technical side of the problem while ignoring the economic side of the problem: you can't have a discussion about changing the blockch

This (maybe) addresses the technical side of the problem while ignoring the economic side of the problem: you can't have a discussion about changing the blockchain without discussing block rewards and transaction fees. Does each branch of the tree get the entire block reward? If so, then you've going to have an explosion of branches. If not, and each mined block earns, say 1/Nth of the reward for N branches, then you most likely go back to a single chain of single-block merges, because each miner is going to try to force N back toward 1. You also need to address the incentives around mining the merge block. If these incentives are not drawn from transaction fees, then you are forced into an inflationary currency.