Yes, I confess I actually do own two Intel Macs, an old 2007 Core 2 Duo Mac mini running 10.6 which mostly serves as a test machine, and a 2014 i7 MacBook Air which I use for taxes and Master's program homework. The MBA reminds me regularly of why I preferred the New World Power Mac days, and why my daily drivers are still all Tiger PowerPC. Lately every year when Apple issues their annual update I get a bit nervous because their quality assurance seems to have gone right down the pot -- I think the beta testers just twiddle a couple buttons and call it good for golden master, and never mind when everyone's machines explode because they might actually have customized it a bit, or something similarly empowering that Apple doesn't want you doing with your overpriced appliances. (More on that when we get to my overall gripe at the end.)
Part of what makes my trepidation more acute is that I actually do write software that can run on a current Intel Mac from time to time, despite my reputation as a Power Mac-clinging troglodyte. Now, this software is still truly Universal in the strictest sense of the term -- I build on my G5 against the 10.4 universal SDK to make applications that generally run on any Mac OS from 10.4 till now, on any Power Mac and on any Intel Mac, and I even found a version of SDL 1.2 (1.2.14) that happily runs in the same environments on all systems without tripping any deprecation warnings so far. I'll be talking about one particular app in the very near future because not only is it Universal ppc/i386, it also includes AltiVec support, so it's actually 750/7400/i386. Keep an eye out for that column. Fortunately El Capitan didn't break the ones I write based on that environment.
Next, I turned to GopherVR and Mosaic-CK, my rebuilds of two venerable Motif-based X11 applications (the GopherVR client, allowing you to view gopherspace graphically, and an updated port of NCSA Mosaic that doesn't immediately barf on newer pages). These use a special launcher program to install a Dock icon and transfer control to the binary under X11. They both crashed immediately. I looked in the console and found that they were unable to run OpenMotif, which they should have detected, but I said no problem and got out my installer of IST OpenMotif 10.5+ which worked perfectly in Yosemite. On El Cap, it wouldn't install.
Why? Blame the new System Integrity Protection, which amongst other things blocks write access to certain directories, in this case /usr, even if you're root ("rootless protection"). OpenMotif expects to install itself to (more or less) /usr/OpenMotif. El Crap won't let it.
Now, you can keep your superior security snark out of my comments, thanks. I get why SIP exists, because users are stupid, and SIP saves them (somewhat) from themselves. At least so far, unless some gaping kernel hole is discovered, it looks pretty hard to toast an SIP-locked installation other than via hardware failure, and yes, if you're willing to jump through a couple hoops, you can turn it off. But you don't have to be particularly clairvoyant to realize Apple won't let you do that forever, and even now it's mostly all or nothing unless you turn SIP off and tinker with its configuration file. Frankly, making users go to all that trouble isn't a good way to distribute software.
So the first thing I did was patch OpenMotif to run from /Applications, which isn't protected (yes, /Library might be more appropriate, but I had to patch a couple paths embedded in the libraries in place and the length matched better), by changing all the linkages to the new path with a Perl script I dashed off and doing a couple direct binary changes. It looked sane, so I put it in /Applications/OpenMotif21 and rebuilt the apps on the G5 to link against that. It worked fine on 10.4 and 10.6, but on the 10.11 MBA they still crashed.
This time, the OpenMotif libraries could be found, but they were linking against /usr/X11R6, because that's where the universal X11 libraries are in the 10.4 universal SDK and every version of OS X from 10.5 to 10.10 had a symlink to /usr/X11 so it all just worked. Guess what new version of OS X doesn't? And guess what version prevents you from modifying /usr to add that link because of SIP?
I toyed with a couple solutions, but the simplest was to lipo a second i386 binary from the main one (since all Power Macs will run the original binary pointing to /usr/X11R6 fine) at the time the app package is built and rewrite all its linkages to /usr/X11 instead. Then, when the launcher starts, it figures out which binary to run depending if /usr/X11R6 exists or not, and transfers control to that. It's ugly and it bloats the app by about 25%, but it's transparent to the user, at least, and it doesn't require the user to have developer tools installed or I'd just have the launcher do the stripping and rewriting on the fly.
After that, I fixed a couple more bugs (including the original one where I had a short-circuit in the prerequisites detector) and packed everything up for distribution, and now you can use GopherVR and Mosaic-CK once again. Make sure you have X11 or XQuartz installed first, and then grab my patched OpenMotif from SourceForge (choose the 10.4 package for Tiger, or the 10.5 package for Leopard through El Capitan). Just drag the folder to /Applications without changing the name or any of the contents, and then run either GopherVR and Mosaic-CK's launcher app, and it should "just work" on any 10.4+ Mac just as it did before.
Why does SIP annoy me most, though, aside from making my binaries more complex and my headache larger? Simply put, I don't like the feeling I don't own my computer, and I'm getting that feeling more and more from Apple. I feel this much less on my Tiger boxes because I can patch them up manually and improve their security and functionality, or alter the way the OS is laid out to suit my taste and needs and how things are installed and activated, and I'm quite sure Apple has great concerns about allowing that on what they consider to be an "appliance." In fact, the irrepressible cynic in me suspects part of SIP's purpose is not just security -- it also has the (to Apple) desirable side effect of forcing most systems to exist in a specific uniform state so that installations and upgrades are more deterministic instead of allowing a (dangerously?) clueful user to muck about at will. While predictions that Gatekeeper would become locked in stone and unsigned apps would be never be allowed to run even by request have not yet come to pass, a lot fewer people will be inconvenienced by SIP than by Gatekeeper except for nutbag tinkerers and hackers like me, and Apple has little downside to making it permanent in a future version of OS X. That means one day you may not be able to change the OS at all except through those changes Apple authorizes, and that would really suck. It would also drive me to Linux on commodity hardware, because if system limitations mean I can't find a way to run my custom apps on a current Mac that run just fine on my G5 daily driver, then why have a current Mac? As it turns out, I'm not the only one thinking about that. What's Apple going to break next year, my legs?