I want to suggest something controversial:
Instead of XMR promoted as an alt-currency it could be called the first "privacy plug-in coin". It's not intended to totally replace BTC. XMR offers features that BTC can not do. XMR's blockchain can't be monitored in the same way and as a result allows anonymous payments.
XMR's killer app will be a distributed exchange that will trade XMR/BTC/altcoins. By trading in and out of XMR you re-enable privacy for BTC! Both coins may thrive off of each others success. As demand for privacy increases the more volume in the XMR/BTC pair.
XMR can be a huge success even if no one uses it as a currency. LTC always sold itself as bitcoin's silver. XMR is bitcoin's privacy plug-in. Poloniex is adding a bunch of trading pairs. I'm expecting that any coin that doesn't have anonymous payments will eventually pair with XMR to enable privacy.
This would create a unique situation in which coins will lean on XMR for privacy. Coins will be able to add privacy without worrying about their blockchain and as XMR copes with challenges in it's implentation, it can idependently change fees, etc to meet challenges. By evolving and using new strategies XMR can be THE PRIVACY PLUG-IN.
I'm not sure its that controversial
I dont see XMR as an ecommerce currency to rival BTC, except for market sectors where people want to remain anonymous and at a distance from the transaction, so no worries about how many confirmations are necessary - merchant can wait for 100 confirms and still ship same day. I think you're right about people trading in and out of XMR, it should be ideal for longterm hidden holding and easy to convert a small portion into BTC for day to day spending money.
Seems to be the way BTCdark is thinking now too, although they are talking about a pNXT exchange using Cryptonote to anonomise transactions, which sounds a bit like they are retro-fitting a solution which is already available in the alternative format you describe above. I may be unfair on them though, havent examined the proposal in depth.