Developers routinely rely on this fragmentation for more options in the feature set vs. price product space. Such a merger will most certainly lead to some edge case configurations go missing. Lowered prices may be the only actual upside - if it materializes in the light of shrinking competition.
Exactly. This market demands that to find the right fit for a product and best value in performance/IO/watts/dollars. More options is always good for us. Anyone wanting to learn less can stick to one product family.
Atmel's and Microchip's architectures are so different that I wouldn't expect any consolidation of platforms.
Less companies means less wooing for end users and thus - a general quality drop in the long run.