There are a few major things people want from computers (in no particular order):
1. Get work done.
2. Play games.
3. Communicate.
PCs are only good at communicating when your at your home. Tablets have the same problem. Netbooks and laptops are more mobile, but awkward.
Essentially if there is anything 'beyond phones' it's going to be nearly disposable tablet-like terminals. Pick it up, login, use it, then leave it for the next guy. After that implants into your eyeballs or something like that.
The Linux desktop is behind the eight-ball because of the technical problems and fragmentation that people refuse to address and instead try to patch over with package management systems. The web is good for Linux desktop because it takes the distribution of applications out of the hands of the distributions. It eliminates the middle man.