Sony alpha a7
Sony's recently announced full-frame flagship a9 camera is a game changer for mirrorless systems. Designed to compete directly against the Canon EOS 1D X Mark II and Nikon D5 DSLRs, Sony has seemingly solved some of the major complaints of the a7 series and mirrorless systems in general.
It has been very interesting to see a slow migration of highly respected professionals to Sony over the past few years. Everyone from Michael Yamashita to Ben Lowy can be found using the systems, so it's clear that multiple thresholds have been crossed with regards to build quality, IQ and glass availability. This includes the general fear that EVFs aren't good enough compared to an optical viewfinder.
Sony recently also displaced Nikon as the #2 camera brand for full-frame systems, which is both scary and a cause for celebration.