One thing I wonder about is this: With Armadillo, you need to place the commit-to-parents vector directly in the Bitcoin coinbase input, right? That means that unlike classical merge mining where you have a Merkle tree of mined chains, you can only merge-mine so many (a rather small number) of coins with Armadillo.
About "classical" merge mining: namecoin defined a scheme which AFAIK did not work well for more than one merge-mined chain. No other project simultaneously adhered to this scheme.
"specs" here:
https://en.bitcoin.it/wiki/Merged_mining_specificationWhile 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.