I reckon looking at the changes they are making this year that picking default apps could happen in the future. They have changed tack on a lot of similarly closed down bits in the OS.

Some people who talk about being able to pick the default apps for protocols seem to assume that it is a five minute change for Apple to provide it. There would be significant engineering effort involved to put in a sensible mechanism to make it happen, it isn't like they've already implemented it and just turned the feature off !

(I'm not saying you're one of "those people", I just get irritated when I see people who do assume it is a trivial change to make)