[jacksond]

First things first, mobile is not dying out. It will be an increasingly large portion of application development for a long time, all of the major players are deeply committed to mobile.

I would not worry about gaining 'unusable' experience. Working in IT/Development means you need to be constantly learning. Gaining experience with the hot platforms (iOS/Android) now will only make it easier to adapt to future mobile advances.

Like I said, the mobile market will only increase in the near to mid future. Anyone entering the mobile space will need to be aware of how to more effectively server their users/customers in a cross-channel and cross-platform way. I believe you can't go wrong with focusing on becoming a mobile expert, if you are passionate about what it offers.