A genuine return to the ease of the Power Mac cases or even the G5/Mac Pro cheese grater.
I owned two G4 (Gigabit Graphite, Quicksilver) towers and I just got that Octocore Xeon 2008 Mac Pro, and point is, I was running Leopard on the G4s in 2008, I kid you not, and my 2008 Mac Pro runs better than my 2012 Mac Book Pro.
I needed a dedicated editing rig and I have never had anything as fast or as capable in Premiere as the 2008 Mac Pro. And I can still toss significantly more RAM in, upgrade the processors to 3.2Ghz from 2.8, do RAID 0 fun stuff, upgrade to a far more capable set of GPUs, etc. There's no telling if it'll run 10.13, but it sure as hell is fine in "unsupported" 10.12! And I'm generally going to assume it will, with a sufficient patch of some sort.
This was an insanely expensive machine in 2008 (looks to have been about US$4000 from my research), and I paid a tiny fraction of that, and with small upgrades of what I had lying around, it's still super capable. Hard to believe this is a 9 year old machine from my vantage point. And given the upgrades, I'll hazard to guess it will last quite a few more years.
Apple needs to make me something I'm willing to drop US$3000 or $4000 on but then will last 10 years. I'm extremely conservative, I change very slowly. I drop programs with great resentment, and I've only JUST started working with 720p and 1080p at 60FPS in my projects. My last significant project was still 480p. I just want to be able to slowly add capability over time. With Apple's current offerings... I can't.