Shapeshift.io just added XMR support and it looks like the database is one step closer. Development wise it looks like there are good things on the horizon.
Shapeshift announcement:
https://twitter.com/ShapeShift_io/status/585570515139563521
Pull request to merge database into master:
https://github.com/monero-project/bitmonero/pull/256
Timing-wise there are potential issues with that
1.123 BTC -> XMR -> 1.122 BTC over a short period of time might be fairly obvious. Of course it depends not the amounts and the level of activity on BTC at the time. If BTC has 1000 tx/sec that would be a lot more obscure than currently
So clearly the solution is to go 5 BTC -> XMR -> 1.22 BTC.
( XMR go.... to... alpha... centauri....)
You can't do that with BTC -> ShapeShift XMR -> XMR.to unless one of those services were taking a 3.78 BTC fee (not recommended to use such as service). You would need to use your own Monero wallet in between.
Also, I'm not sure what sort of mix factors and such being used by shapeshift, so the normal caveats about Monero being optionally anonymous (and not fully mature) apply. Again putting your own Monero wallet in the middle and being careful with timing could give a better result.