There is very convincing research that Epstein Barr Virus causes Multiple Sclerosis, and the current treatment I am on for MS destroys the B-Cells the latent virus lives in. I think you're spot on, infections are probably the cause of most of these auto-immune diseases.
In MS we're getting closer to finding the cause and ultimately the cure. It does take a while for research to get funneled to the right person with the right specialty and right funding -- sometimes years, decades.
I'm not sure tying the diseases together would be a winning strategy...? My MS could be caused by the EBV living in B-Cells and a genetic or environmental (or both) trigger. Your UC may be caused by a certain bacteria living in your gut triggering a T-Cell response by a different genetic or environmental element.
And yeah, the doctors don't want to hear my pet theories. hah. I have done my own labs, brought them in, and the doctor just gives me a condescending look like - why are you even trying? I guess they don't know how desperate most of us are for answers.