That is a very interesting development. I know it's not getting anywhere close to x86 (_64) open specs or some other ARM-powered SoCs, but QualComm constantly shooting themselves in the foot by closing it off and not even selling the SoCs hasn't been very productive in the low-power computing community (and industry). I get that the first instinct of NDA-driven businesses is to ignore makers or community-based hardware designs (and sales), but with the Pi selling about 10 million, it should be getting harder to ignore what used to be 'the little guys'. With innovations basically taking place at hacker's homes, not being available basically makes you useless in the sector where your chips could be great.
For Broadcom, the Pi might not have been such a big deal, a single home use router with a Broadcom SoC might easily sell 50 million units, and there are plenty of home use routers for sale with Broadcom SoCs in them (let's say, we have 100 brands/versions, that's at least 5000 million chips sold over ~10 years), but the brand name and support from the community (which is bigger in numbers as well as diversity than any of the big tech companies) is pretty much priceless when you hit that millions number and up.
I hope QualComm and their Snapdragon isn't the last one to nudge closer to availability, there are plenty of others that would be welcome to join. While being able to buy the chips themselves isn't the biggest improvement, the fact that they are actually interested in helping with some open drivers is a major improvement!
As the x86_64 world continues to get more locked down, it's going to be interesting to see whether a market niche opens up for a less-constrained platform.
It's confusing to me that you're calling it "less-constrained." The signed-bootloader world really caught fire in SoCs like Snapdragon and indeed the 410E and 600E include SecureMSM/TrustZone. It hasn't (yet) found big popularity in x86_64 designs -- even when the processors offer it many customers don't leverage/enable it.
The "locked down" designs come from two big motivators: DRM and security. Since many snapdragon phones are sold with subsidies, the signed bootloader allows the network operator to restrict the phone's "owner" in various fashions. The security provided by a signed bootloader is real -- it's much harder for a malicious actor to create ransomware that targets mobile phones like they do PCs.
I'd expect/hope that you can decide not to opt-in on the Snapdragons' SecureMSM features, but it doesn't seem any "less-constrained" than Intel or AMD's offerings.