Prior to my 2010 MBP, I upgraded every 3 years on average. For my Mac Minis I upgraded every 6 years ending in 2012. Since then not one upgrade, Apple is not making pro or top level machines anymore. The last one IIRC was the 2011 17 inch MBP and the 2012 Mini. I am waiting for this years WWDC and if we don't see pro hardware, then i'll have to go elsewhere. Not sure where, but elsewhere. I am sure Apple does not care.
Since Apple outsourced Swift, I think they are moving to become only a phone and tablet maker. I think they will move their development tools to linux or windows and stop making real computer completely. That seems to be the trend. Remember they moved all their data center hardware to linux and greatly reduced mac os x server. While that makes some sense, since OS X was never a server OS. it is still troublesome.
I really do not think that is the case. Now they less and less support the professional market. But with Mac sales increasing I really do not see them leaving that market. Also remember they have to actually do their work on computers. Is Apple going to walk away from a profitable business (one where they make billions every year) to also put themselves in a position where they have to actually do their work on a Windows machine made by HP or Dell? Do you think they want to walk into coffee shops and see tons of young folks with booted up ChromeBooks? Are they going to abandon the billions they've spent on OSX? No way.
Also if you go out and start buying PC hardware you may find yourself very disappointed. Sure the CPU and the GPU will have the latest specs. But if your experience is like mine you will find that the actual integrated machine is going to have issues and serious durability problems. My company bought a bunch of nice Toshibas and most have failed in one way or another within less than two years. Considering the lack of profit that PC manufacturers are making these days, I suspect even more corners are being cut now in 2016. If the PC market continues to shrink I don't know what value I can actually get when I buy a $1,300 PC laptop in the future.