So why don't you try 64bit, or are you on a 32bit OS?
My main reasons are that I'm worried about the risk of having issues if I keep playing my current world on a newer version, and from what I've read it seems Dwarf Therapist doesn't work properly on 64-bit.
I'm honestly not sure what it is. My best advice would be to disable all of the plugins (really disable them, with the "disable -all" command, not through a pack), and then re-enable a few at a time until you find one that's crashing.
Neither disable -all nor "disable -all" as commands seem to work, but I can disable each of them manually in the init file. Stonesense and Tweak won't disable though ("Cannot disable plugin: stonesense"). Regardless, that still crashed.
I then tried just commenting out everything in the 3 init files I found in my folder (I have additional dfhack and onMapLoad init files with PeridexisErrant's name), but that also still crashed.
Then I just renamed the hack/plugins folder entirely. Success! Saving also works. Guess I can create a new empty plugins folder and manually add the plugins one at a time and see how that goes.
Edit: The folder has 83 plugins. Loading the first 40 works, and loading the last 43 *also* works. Either there's a conflict somewhere, or I'm just seeing a re-hash of the last times I got things running again, namely that I'm just getting things to work by trimming down my game environment and freeing resources, without actually finding a root cause.
Final edit, hopefully: Putting everything exactly as it was before, but without stonesense in the plugins folder, seems to work. It does happen to be the plugin with the largest file though, so that could be a coincidence, especially since enabling TWBT is still causing a crash with that setup. And to be clear, I was not actually using stonesense.