The advantage of cannon and Sony is that they are conglomerates and have the resources to develop new tech in-house. With the transition to digital that burden is high for the independents so they’re always playing catch up. If I were buying today I’d likely buy Sony (or perhaps canon), I don’t see a future for the rest.

That said I think Canon and Nikon had some kind of IP agreements and shared some technologies, or I may be wrong.