TL;DR: Check out DarkTable.
I'm surprised DarkTable isn't mentioned more. I've been transitioning from Aperture to it over the past week or so. Learning a new workflow is a bit like learning how to walk all over again, but as a product I've been pretty happy with DarkTable. The edits are non-destructible and the software is really powerful. There's a learning curve but between reading the manual and watching some videos on YouTube I'm picking it up.
I think I'll probably export out my aperture photos to high quality jpegs eventually. I seldom ever go back and re-process old photos, so having them "locked" into jpg won't be that big of a deal.
I start by copying the RAW images into folders (via Image Capture or just using finder) using the same naming strategy I used in Aperture: YYYY-MM-DD <Description>. Then I import the folder into the software as a "roll." I'll go through the roll and reject obvious trash images, then rate the rest: images with 4 or 5 stars are obvious "good" shots, while 2-3 stars are left for later consideration. I'll post process the 4 and 5 star images to my satisfaction, then export what I want to share as jpgs to a separate folder. (At some point I'll go back over the 2-3 star images and decide whether or not they're worth keeping and working on, or if they're just duplicates of a 4 or 5 star image. More often than not, it's the latter.)
Right now I'm importing the jpg's into Aperture to share the pictures to an iCloud folder or Facebook or whatever, but eventually that will be replaced with the Photos app. It'll serve as a repository for my final product(s), keeping all of my best images synchronized across devices and to social media sites. The original RAW images with their sidecar edits will stay in their folders. (I did change Aperture to simply point to the jpg finals instead of importing them - no need to duplicate the space used.)
I'd already been trying to keep my photo storage relatively "clean," even in Aperture, by parsing down to annual "photo albums" - each completed year I'd go through and only keep 300-400 of the best pictures from that year and delete the rest. To save myself from going through thousands of photos once a year, I've been pretty good at habitually purging photos from individual shoots at the end of my post-processing workflow that didn't make the cut. It's kept my Aperture library pretty lean.
I then share the annual photo album out to an iCloud shared photo stream so that it's available online and I can share it with family if I want. If something happens to me, I know that my wife/kids/family has access to our photos without having to learn how to use a photography DAM. Again, that's where the Photos app will come in - not as a post-processing editor, but simply as a tool to share and synchronize the best photos I have.