Freelance. I have a home studio.
I edit independent films shot on various cameras – 1080p DSLRs up to 5K RED.
I create motion graphics for broadcast and streaming corporate communications/marketing.
I also create PowerPoint decks for corporate clients.
I have a lot of friends who are editors, cinematographers, color graders, sound designers. I go to film festivals and meet those kinds of people from all over the world.
One friend of mine does FX with high level software that uses Octane Render, etc. He worked on a few big Hollywood movies. His #1 complaint about Macs was how much slower at rendering they are compared to PCs.
I have a few Macs including a 2007(?) Mac Pro tower. I've been able to upgrade that Mac Pro for 9 years now. I've upgraded the video card three times, and I put in a SSD drive that goes into one of the PCI slots. It boots in seconds and apps launch lightning quick, on a 9-year old computer. The resell value of a 2012 Mac Pro tower is very high, to this day, because people are buying them and putting in the latest nVidia graphics card, SSD drives, etc. and those are faster than the latest Macs that cost $5K and up.
OK, what you do and how you do it make my point. I live in a city with a strong creative community, mostly music types, and lots of them Mac users. I have many friends like you and your needs mirror them. One friend specifically has only bought Mac Pro type machines since the original Mac II become available...and I should know, I set it up for him when I was in college. Today his studio has numerous Mac Pros (he works alone) that are usually all 2009-2012 vintage. He's retired a 2006 and 2008 recently which he gifted to me (the 2006 is powered off, the 2008 is a new server in my house hacked to run High Sierra). This guy also still has a PowerMac 9600 in production that is hooked up to a specific film scanner still running Mac OS 8.6. I told him that if the hard drive (now 20+ years old) ever failed, I doubt I could ever get another one for him.
The point is that like you, he buys modular Macs and keeps them for a very long time. He upgrades video cards and memory if necessary. But he is dead set against going the hackintosh route since he depends on the reliability of the platform. Case in point...I recently built a brand Windows PC tower for him for the sole purpose of being a dedicated flight simulator computer driving three 65" curved Samsung 4K TVs. We spent about $4K on parts for the machine alone (including X99 ASUS mobo, Intel Xeon 6950 with 8 cores, 32 GB of RAM, 2 TB of flash memory, two Nvidia GTX 1080 cards). And even with high quality off the shelf parts from major vendors and the latest Windows 10 from Microsoft, it took me 3 months to get the machine completely stable, even without overclocking. He would NEVER tolerate that for a production machine for his photo business. Even the 2008 Mac Pro he retired was disposed of because it wouldn't boot anymore. Turns out the problem was a failed memory DIMM that he'd installed himself a while back.
Smaller outfits and indies like you are used to buying a machine that has an upgrade path down the road to keep it in production as long as possible. I am also like that since my house is full of hardware kept alive long past the point most people would keep it in production. But when you open a chassis to make changes, you always run the risk of screwing something up. For people like you and me, it's a risk we regularly take. But I also work for a very large company who would never bother taking that risk for user machines. We've even gotten to the point where we don't allow companies who buy our servers to make memory upgrades to them anymore...too many times we've seen a machine that doesn't survive an upgrade to a mission critical system (and yes, I've seen this first hand).
Your friend complains about the speed of professional Macs....is that really a shock? The 2012 Mac Pro is indeed like gold these days since it's the last machine you can still stick a modern Nvidia video card in. But the Xeon technology including the memory bus and all supporting systems are over 5 years old, which is an eternity these days. The 2013 Mac Pro is better but again, we're talking about 4 years old (not counting the most recent spec bump). Compare that to the Flight Sim rig I built and that's easily the fastest machine I've ever had in my house, going away. And of course, the top of the line 2017 iMac (not Pro) is faster single threaded than the 2013 Mac Pro and is competitive with that machine out to 4 cores before the Mac Pro finally starts pulling away. Why? Well, time marches on and it's not a surprise that consumer grade chips will eventually match or exceed server grade Xeons.
I do think you will get a Mac Pro that you will consider something "for you", probably in six months. I think Apple has learned that lesson. There has been a tension at Apple on upgradeability versus "appliance" since the first Mac 128K appeared. Before that, everybody was very used to cracking open the top of their Apple ][ and making changes. Apple couldn't have gotten to the point it is if it still built everything for tinkerers like us. But we are still an important (and vocal) minority of users, especially in the high profit pro space. But please understand that not all "Pro" users have the same economic model that you do in terms in technology purchases. The iMac Pro is for them, not you.
