"mobile" also means more than just iOS and Android, although they're the two dominant platforms today.
The whole point is to allow different apps to be swapped without the others needing to change. All this does is tie everything too closely together, and more likely than not to Facebook.
There's really not a lot going on here. Webpage scheme that you can parse to build an intent from. This couldn't be more than 50 lines of code. It would be less if they decided to use a custom URI scheme like "applinks://example.com?packagename=example.com" instead of parsing every webpage you go to looking for the applinks headers.
So Applinks suddenly removes the ability of 3rd party apps to say "we can handle this content". I can see why big players like FB would want it - I think this is a bad thing for small players and hence the open ecosystem.