After being an Apple "Loyalist" for over 15 years, I recently sold my rMBP and built a desktop (i7 4790k, GTX 1080, 16Gb DDR3 @ 2933Mhz). It was by far the best hardware decision I have ever made. Building the system was an absolute blast. Plus, I now have an extremely powerful PC with first class Linux support, tons of I/O ports, and no vendor lock in. The best part is it cost me about 1/3 of the price of a (maxed-out) Mac.
As for portability, I bought a ARM Chromebook and installed Xubuntu. I also have an iPad and iPhone. The three get the job done.
The toughest part of leaving OS X was knowing I was also leaving hobby OS X and iOS development. And homebrew. Man, I will miss homebrew.
I am puzzled about missing homebrew..
You said you are installing Xubuntu, which comes with an excellent package manager with less issued than a brew user is likely to run into.
For a lot of popular packages homebrew is more bleeding edge these days than whatever the default sources are for Ubuntu. It's nice not needing to add a bunch of extra apt sources to get updated packages. Another perk of homebrew is, in most cases it can't really screw up your system. After all these years apt can and still frequently does break things. Just the other day I had to help someone restore an apache config that got hosed due to apt upgrade trying to remove a package. It's in an endless loop of insisting the old package has to be installed before it can be removed or some such non-sense. Of course as you might guess this person's apt sources were full of random things that he most likely found and copy & pasted from random Internet sites. Somehow he had what I guess was a docker nightly build which, when updated, caused all the containers on his machine to be stopped. He thought docker was just buggy and crashed a lot. Good stuff. I very rarely have any of those problems with homebrew.
I think it's probably because Homebrew has all the obscure packages one might ever need, and packages in Homebrew are quite up-to-date even though it may not be extensively tested. For example, I use cocot quite often (for dealing with SJIS systems), and while cocot is in Homebrew, it's not in the Ubuntu's official repository.
I'm pretty sure AUR has everything :) But the OP was talking about ARM, which I'm not sure about the state of ARM port for Arch Linux. It's also true that one can also find PPA, but there's big convenient when it's installable right away without needing to search for PPAs.
I was in a similar place but ended up getting a MacBook in addition to the custom PC. Most of my day-to-day work just feels more efficient with the Mac but I realized that it didn't make sense to rely on a laptop for gaming, video encoding, and media serving. I still love the Mac for Final Cut and all that, but I just had to change my workflow a little and now I get the best of both worlds.
This is what I did, never been happier. My current desktop is the most used and useful possession I've ever had.
I don't have a Chromebook, but seriously considering it if I can use Dropbox and a terminal on it for dev.
I still have a MBP for work, but it has become a chore to use especially with Sierra breaking everything (iCloud is now incapable of working with our company's security software or something)
Out of curiosity, if you are such a OS X/homebrew fan, why not try a Hackintosh setup?
I don't know if you can get a dual-boot working well with OS X, but worst case scenario you can have a HD for each OS (after all, you have a desktop now and no longer a notebook) and boot the Linux disk in case the Hackintosh starts to show any signs of trouble.
As for portability, I bought a ARM Chromebook and installed Xubuntu. I also have an iPad and iPhone. The three get the job done.
The toughest part of leaving OS X was knowing I was also leaving hobby OS X and iOS development. And homebrew. Man, I will miss homebrew.