I'm wondering if it's possible to use a sidechain to effectively bind two dissimilar chains together. If that's possible you could use bitcoins to run ethereum contracts and use ether to send money to a bitcoin wallet. Both systems would do well; Bitcoin for its brand recognition for digital finance, Ethereum for its generalized scripting capability.

edit- looks like I found my answer: http://bitcoinmagazine.com/12349/side-chains-challenges-pote...

I think the future will see all of these systems interoperating and we'll no longer be debating popularity.