My very first camera, about 40+ years ago, was an Asahi Pentax SP1000 - a high quality, reasonably priced beginner camera. It had a screw thread mount and a great selection of Super Multicoated Takumar lenses.
I left the Pentax gear in a Don Mills parking lot about 10 years later while going to a view camera class at Sheridan College. Long story short, I got my gear back but not before I bought my first Nikon single lens reflex, a used FM and the legendary Coke bottle 43-86 zoom. I've been using Nikon since then, buying another FM and an FE, and adding various Nikkor, Sigma and Tokina lenses to my arsenal. All of which I still have and all are operational.
After being away from photography for a few years, my interest was rekindled by digital. I bought a Kodak point-and-shoot first and then made the leap to a Nikon D80 in 2007. Why Nikon again? Because I had all of these Nikon mount lenses that fit the D80. Yet, I couldn't meter the lenses with that body. I made due until 2011 when I used some inheritance money to purchase a full-frame D700 (great camera, still using it!), some lenses and, eventually, a D600 to play with video.
While the newer Nikon bodies and lenses have been great, and probably optically superior to many of my older manual lenses, they just aren't built like those metal FMs/FE and Nikkor lenses. Several lenses have either quit on me or are in a state of disrepair. The LCD display on the D700 is cracked. The local camera tech could not get parts to repair a four-year-old Nikon 135 f2 DC. Understand that I'm not a globe-trotting journalist covering foreign wars; I'm an advanced amateur who led camera clubs and photo walks.
So, the news that Nikon released a new mirrorless camera with a new, incompatible lens mount was greeted with a "ho-hum". Sure, this is Nikon's first real mount change (not counting the discontinued Nikon 1s). Canon is on its third mount over the same period of time! I understand how the old mount constrained innovative lens design; I heard all that when Pentax dropped the screw thread.
I know I can use my Nikon F mount lenses with an adaptor. I can also do that on a Sony body. On a Fuji body.
At the end of the day, if I'm looking at a set of new bodies and lenses, I could buy anything.
I no longer have brand loyalty.