Update!
So, instead of picking one or the other, I simply went with both. I now have a Magpul MOE M-lok handguard on my AR pistol, and went with a 10" keymod rail for my lightweight rifle build. The keymod rail came with six 3" sections of rail, so I'm goo to go there probably til the end of time. I haven't yet mounted anything to it yet, because I like the slim profile and light weight of the tube itself, so just have a MBUS front sight on the hand guard. Nothing else. But I have options in case I do want to slap accessories on it.
I don't yet have any M-lok rail sections, but have plans to get a matching OD Magpul M-lok stubby front grip once I get my Form 1 approved. That'll probably be the only accessory the M-lok adorned AR pistol/ SBR will get. But I am thinking of a quality weapon light to mount, as well.
For now, I'm glad I went with both. No real need to standardize, and I like having options.