A belated update - I had a long exchange of emails with a guy called Flint in Zwift’s support team, who was probably as helpful as he possibly could be, but it was clear that his hands were tied by some nonsensical support policy and he was basically powerless to help despite good intentions (or at least reached his personal limit of tolerance / patience in hammering on some internal engineering team).
The last email I wrote was as follows:
Thanks Flint, totally understand your position, and I really appreciate your honesty on this. I’m still very dubious that there is any valid technical reason not to support the Pixel Slate or other Chromebooks, but I’m perfectly willing to be persuaded otherwise, and certainly don’t want to shoot the messenger here 
From my perspective there are three acceptable outcomes:
- The engineers perform some quick triage to establish why the Game tab is not appearing, discover it’s as easy to fix as I suspect it is, and fix it. This is obviously the ideal outcome, and I would be perfectly happy even if I had to wait a few months for it.
- The engineers perform some quick triage to establish why the Game tab is not appearing, and discover it’s too hard to fix to justify the effort relative to other higher priority items on their backlog. Zwift then provides a public statement (not just to me) explaining why this doesn’t work, which devices it affects, and why it’s considered too low priority to fix.
- The engineers already know why it’s not appearing, and Zwift provides the same public statement as in 2. above.
The second and third would obviously be disappointing to me, but still reasonably acceptable first steps although not a full solution.
In addition, as an extension of the above point about making public statement, Zwift really needs to properly document which devices the Companion app supports. I have looked on your website, and I can’t find any useful information on this. For example, support.zwift .com/en_us/categories/what-you-need-to-ride-BJjM4TyeH doesn’t even mention Companion once! If I follow the link to support.zwift .com/en_us/supported-devices-to-run-zwift-H1Cj9QbeB it still doesn’t mention it. I can only find useful information on Companion by searching for it. That leads me to this page support.zwift .com/en_us/using-the-zwift-companion-app-rJ7ayD_ES which again says nothing about which Android devices are supported. The implication is certainly that any Android device is supported. (Even though I won’t personally pursue this angle, I think any paying customer could reasonably argue they were entitled to a refund on grounds of buying a subscription on the assumption that they would be able to use Zwift with the Companion app.)
There are also some outcomes which I would definitely consider unacceptable, e.g.
- The Companion app is retracted from Google Play for Pixel Slate devices without any solid technical explanation of why it is any harder to support them than any other Android devices.
- Nothing changes with the app, and no solid explanation is given.
- The website is not updated to clarify on which devices the Companion app is supported.
I want to emphasise the importance of getting this right, which may be underestimated due to the Companion app being perceived as a “freebie” or unnecessary luxury. This perception would be incorrect, because Companion is absolutely crucial to the functioning of Zwift in certain circumstances, including mine: I run Zwift on an Apple TV and rely on Companion to overcome the limitation around transmitting data over Bluetooth from my sports devices. We customers need to know this kind of thing in advance, before we purchase a tablet or Zwift or any related devices. That’s why it is not sufficient to simply retract it from Google Play, for instance.
So I hope Zwift can manage to avoid these last three, which in my opinion would constitute disappointingly poor customer service. I do appreciate that you are personally limited in how much you can influence the situation, so again please don’t take this as me shooting the messenger 
Finally I wanted to offer some thoughts which of course you are free to ignore if it doesn’t resonate! You wrote “there is just a certain amount of need-to-know when it comes to these types of things”. I’ve worked for software vendors for 15 years, and yes I have experienced this. But the question is - what level of need-to-know is appropriate? Personally I think that unless you are working for some organisation which handles highly sensitive information and has a strong need to keep things confidential (e.g. military / certain government departments), secrecy often hurts more than it helps. Certainly in the case we are talking about here, I can’t think of any good reason to hide any internal conversations from you, your colleagues, or even from customers like me. If there truly is a good reason for not supporting the Pixel Slate or other Chromebooks, then making that explanation available to us would still be far more satisfactory than not addressing it and not explaining why it won’t be addressed. As a customer, feeling ignored is one of the single most frustrating experiences. Clearly you personally are doing the exact opposite of ignoring me, which is fantastic, but if your Android team doesn’t take effective action then unfortunately all your great work would be for nothing. Hope that makes sense.
Anyway, that’s enough (or maybe too much) for now. Once again many thanks for your great support - I really appreciate it!
Adam
(Sorry about the broken links but this stupid forum won’t let me post them properly.)
Unfortunately but perhaps unsurprisingly I heard nothing back from anyone after this point. So the TL;DR summary is that despite some valiant efforts from their support team, Zwift deliberately chose the worst possible (non-)response to this issue, clearly showing that they don’t really care about us Chromebook users. I guess we are too tiny a slice of the market and they are not honest enough to tell us the truth. Extremely disappointing.