SWIM = "someone who isn't me". A way of saying "obviously I mean me, but legally I can't actually say it's me."
So I'd read that previous post as implying that "I worked at Apple but due to NDAs I can't admit that fact, so I'm pretending this story is hearsay." Of course it could also actually be hearsay.
Personally I always assumed the NVidia split was instigated from Apple's side. I can think of various reasons they'd want to lock NVidia out - such as the possibility of negotiating better terms with AMD by guaranteeing they have exclusive access to market for new GPUs in Macs. And the push to promote Metal that the previous poster claimed certainly sounds plausible; I can see them not wanting NVidia to be able to continue with CUDA on Macs and give customers a competing option. Especially as by that point Apple was already secretly developing Silicon, and knew the time would come when Metal would mean Apple hardware exclusively.
Looking at it from the other side, it seems hard to believe that NVidia would just throw away the chance to sell new hardware to Mac users. Especially as it came at the same time as eGPU support was added, so that market was growing. The cost of developing and supporting drivers - drivers that were already written - seems like it would be significantly lower than potential revenue from Mac users, so why not support them if they could? Someone said it was because they didn't want to support Metal, but I don't buy that. In fact that could give them an opportunity to 'prove' CUDA was better than Metal, by optimising the former and not the latter. Which again speaks to Apple wanting to prevent that possibility.
I'm also not sure that it's true to say it was as simple as getting a developer account. Even if that was all that was technically required, that still allows Apple to block notarizing - they always have the final say, and have blocked developers before for various reasons. On top of that I do wonder if there's more technically required in GPU drivers than just following published APIs and then notarizing them. I had thought that developing GPU drivers for macOS - along with necessary support for Apple Secure Boot and the like - would require some help from or cooperation with Apple, but I don't know enough about device driver development on macOS (or in general) to know for sure.
In general I have no problem believing that both Apple and NVidia are quite capable of blocking support for entirely selfish and anti-consumer reasons But in this case it seems to me to be more likely to be Apple than NVidia. And there appears to be some evidence for this beyond the public statement from NVidia,
such as journalists that spoke (off-the-record) to Apple developers.
All that said, I don't see many parallels in that situation and that of AMD 6000-series drivers, besides the obvious one of "we're all waiting for news and have no idea if or when it will come." Apple and AMD have an ongoing relationship, with AMD GPUs being sold every day in Apple hardware and reports of at least some new Intel-based Macs still to be released. The day will come when Apple is 100% using Apple hardware, but we're not quite there yet. I would be pretty surprised if the 6000-series GPUs were not supported at some point fairly soon - though I could definitely see them being the last third-party GPUs to receive support.
Personally I'm choosing to look on that recent post by the Octane developer as a good sign. He'd be better placed than the average person to know about macOS GPU support, and he claimed that 6800/6900 support was imminent. Actually he claimed it was there in 11.3 beta 3, which it isn't (at least not full support), but at least that seems like a promising sign.