I don't think any of us here dispute the fact that there will be DX bodies for the forseeable future. There will always be a D3200/D5200 equivelent for the full "A" mode shooters (and there are far more of them than there are of us). They still make teeny tiny compacts with teeny tiny sensors for the pocket crowd.
But, those cameras simply can't do what we need them to do. My first DSLR was a D50, which I used for five years. I was 100% content (other than the tiny, useless LCD) with it. Then, my kids got older and I discovered action/sports photography. After one football season with the slow focusing, limited ISO performance, and puny 2.5 FPS of the D50, I was ready for an upgrade. I gave up basketball shooting for that year after one shoot with the D50.
And I am purely an amateur, in equipment, dedication, and skill. I'd love to see a D7200/D8000 with better high ISO, or better yet, a D400 with the pro AF system. I just don't see a D400 in our futures. I hope I'm wrong.
As for DX lenses...I have two: 16-85 VR (walk-around), and 35 f1.8 (basketball). I have four times as many FX/Film lenses. If my next body is a DX body, I'll probably pick-up a used 12-24 DX (been putting this off for years deciding if an FX body is in my future). If I ever abandon DX completely, I'll just sell them for whatever I can get. I consider camera equipment like a tool, not an investment. Buy it, use it, upgrade and give it to someone else to use.