Btw, it is my intention with Armory to do exactly what you just said is out of scope. There's no reason to optimize the case of multiple wallets coming from the same seed, because most of the time you don't ever want a single device seeing all the keys. You want your phone to create one key, your computer to create another key, completely independently. In the case of a big organization, you want different branches to create their wallets independently, and swap pubkey-chaincode pairs.
Exactly: swap chaincodes. If they swap their chaincodes anyway they could just as well use the exact same one. (It doesn't make a difference securitywise if they do.)
Plus, if there's, say, a vulnerability in one of the devices' RNG, you'd prefer that it only affect one piece of the multisig wallet.
That's an argument, indeed. Plus, a party may not want to rely on another party's entropy but prefer to use it's own.
There's a lot of possibilities there. While there may some use cases where keys are generated on the same device, that's far from guaranteed. In fact, I think it's the opposite, if we want to promote security best practices.
Yes, lot's of different ways. I'm just saying prepare for the fact that chaincodes will get re-used across different pubkeys. Whether it's for multisigs or some other purpose. Even if it's not the default behaviour for multisigs and even if you don't promote it in any other way, people might still find applications for it and do it. Chaincodes are only semi-secret after all.