Not for another 5 years, I think. Because that's how long all the apps included with Ubuntu 12.04 / Mint 13 will be supported, and most of them work fine with G

Not for another 5 years, I think. Because that's how long all the apps included with Ubuntu 12.04 / Mint 13 will be supported, and most of them work fine with GTK+ 2. I also wouldn't worry too much about what desktop options I'll have in 2017. The options available at that time will probably be very different from anything we have now.