[...] altcoins are interesting for research, but not in foreseeable practice - what I am saying get *something* useable in bitcoin, get people hooked, once scalability issues inevitably show up, transition to altchain.
This ignores the benefits of monetary diversity. Bitcoin might be here to stay, but in the future altchains will be most commonly used as they can be tailored to specific environments, and thus provide the most benefit to a community.
Crosschain p2ptrade is actually easy problem if your altchain is designed to support it. Only place where you hit the blocks is things like LTC x BTC.
Really? Because that's what Marketcoin is trying to do, and it's not that simple. Maybe if you have two altchains designed to work together... but I'm not aware of a way to do that yet. Care to provide an example?