The problem is, they're designing products for general consumer use as the primary reason these days. As much as we dislike it, the hardcore who love the Mac and want open systems to tinker with are a very small niche. I'm honestly surprised they reversed course on the Mac Pro. Smart move though, as even if there's less profit in this niche, you need to appeal to them as they're the ones who will also push Apple products to their circles as well.
Actually, I think the 'open and tinker' is an overlapping, but separate segment of pros. The big problem with the 'trash can' design is GPU-related. It doesn't have enough external bandwidth the kind of GPU power that could be internal in the previous gen, and the GPUs weren't upgradable. That isn't so much about open and tinker, as it is just an inherent design problem and mis-read of the market segment.
For example, lets say they keep the 'trash can' design, but come out with an external add-on for plug-and-play eGPU extendability. I'd guess most pros would be fine with that, even if they couldn't open and tinker. The hobbyist / gamer / experimenter crowd would't be... but those are different people often.
As for timing and 'throwing them a bone' I don't think Apple is quite ready to face the exodus of the pros quite yet. I'm not sure that will still be the story in 5 years. I think they have to do another round or two. But, I'm not going to believe they are solidly committed until I see more work on the software front.
Yes, I think this strange announcement confirms that Tim Cook - and Apple - have zero real interest in pro machines, and that anyone at Apple who did, is long gone. Now they're letting Phil Spiller cobble something together to keep the complaining "pros" happy. How else can you explain Apple going so completely against their usual secretive approach to new products? They're doing this because it's a niche product for a minority of noisy "opinion makers", who they want to quieten down. But in the broader sense, they don't have their hearts in products like this at all. It's certainly no coincidence that Tim Cook wasn't there.
Yes, I see this very much as a damage control effort. Tim's comments and Apple's actions make the farther future pretty clear, IMO. They need to stop the bleeding... for now. And, that Ferengi guy... what planet is he from?

He's certainly not in touch with reality or Apple's Mac base.
Apple has shifted from being a corporation that would do some KILLER stuff, just because it was 'Killer', to a company that seems to be looking over its shoulder and trying to feed the bureaucracy and not the customers. So, in other words, just like ever other corporation that loses it's focus and it's heart.
Bingo. They've lost their soul. It's about pie-charts and profits, not UX and making the best stuff, anymore. And, like every other corporation, they'll now be replaced with someone who is actually innovating and caring about their customers. But, with Billions in the bank and huge brand-cachet, it's going to take a good long time. But, remember Microsoft? Did any of us ever think Apple would even approach the size of M$, let along eclipse them? Apple now has their Ballmer at the helm.
The trash can pro was an interesting idea, but the warped view of 'skinny' has ripped the soul out of the damn thing. Big was good. Air flow is great. Upgradability is amazing. They made a 'box', and that 'box' had little way for improvement.
As I said above, I'm not sure most pros care if it's 'open' or 'closed.' But, it has to meet their needs. The 'trash can' was revolutionary for what it is... it just missed the mark of what it needed to be. TB was mature enough to handle external storage, but not GPU. Plus, it adds a ton of cost to an already expensive system.
I don't care so much if the next Mac Pro is closed, if it's done right. Heck, bring back the 'cheese grater' with new internals. Or, go modular like the 'trash can' with *acceptable modules* and comparable pricing. Either work, but the previous attempt wasn't either.