Buy what you need at the time of the need. Don't bother waiting for what we call "vaporware..."
I've been on the Mac platform since 1984 and the grass always seems greener on the other side, the next announcement, next year...
A friend always would seem to get a new machine about 2-3 months before the newest, fastest, best machine out there. He bitched, moaned, wrung his hands. He always had remorse and would ask me if he should sell what he had and take the loss or what... I would always advise him to turn off the TV (stop looking at the type) and both learn the software and use what he had. Spend the time productively and learn the process down to the nuance! Once you know how it works, then in a couple of years you could take a look to see if the hardware was that much better.
I'm using a 2009-vintage machine now, maxed-out with ram and SSDs, a beefed-up video card and processor. I/O can be slow since the architecture is more than a decade old but I'm only one OS behind the newest and it's both working fine as is the software. It's fast enough for me and does what I need.
Whatever you get today will be perfectly fine for several years in spite of the rumors. Even if Apple goes to the next hardware platform, I wouldn't worry too much. I've now been through at least 3-4 changes in processor architecture and with the exception of a few programs that have eventually been orphaned, I'm still getting work done.
With today's machines, you'll certainly be a step or two beyond me and I plan on using the system I have for another few years. Your system will go even further and no mater which you have, your speed will probably run circles around my "antique" system!
Bottom line, just do it!
