While this is not exactly on topic, I'm curious. Why do you think that the Namecoin scheme does not work and that no other coins would adhere to that scheme? I'm at least aware of three other chains (Namecoin, Huntercoin and Xaya) that all follow that scheme and at least one pool (F2pool) that mines more than one together.
Check it yourself from the algorithm given in the wiki. Also the wiki states this. If merkle_size is a power of 2, when there is a slot collision of slots for some chain ids, then the collision will persist no matter what merkle_nonce you use. I can sent you a code function that checks this by scanning but it's clear from the equations this is true.
So I don't know how f2pool is doing it, it will work if it's merging 3 chains, but not for merging 4.
Ah yes, I've heard of that before. But if that happens, you can still make your Merkle tree larger and most likely not have collisions anymore, right? So this is clearly a bug in the original implementation, but no deal stopper. (And in theory this could be fixed by using a different way to assign slots.)
With Armadillo, you will never be able to put an arbitrary number of merge-mined chains into a fixed amount of coinbase space.
(Note that I'm not saying Armadillo is a bad idea, I just previously had the impression when talking to miners that coinbase space is a concern for them or for some of them.)