By non-fragmentation, I'll assume that you mean the software side, unless you want every phone to be the same.
On the software side, this can only happen if Google takes over the updates for all devices. This would only occur if; A) carriers relent and B) hardware fragmentation goes away. In other words, say goodbye to your choice in hardware.
What Google is doing now is smart. By separating core functions from the OS, Google can push updates through Play Services in a way similar to how Microsoft pushes Windows Updates. However, it's still up to the OEM to update to the latest version of Android, and that level of fragmentation will likely remain as is (because they alter so much of the framework, Google can't update this on each device).