Hi,
5.2 should keep being supported for a while as lots of people use Titan X cards.
The 10xx cards should be as well.
The reason for removing the 2.x support is that so many features are missing that GPU implementation would need to be so different.
Finally for 3.0+ cards, you can still compile from source and use them. It is just not in the binary versions because the number of people using them is low and it makes the binary huge (500MB+).