You can run coreboot with Qubes OS. You can even order a laptop with Qubes OS pre-installed, using coreboot and with IME disabled. However, there are several issues you didn’t mention. For example, there is no officially supported true deniable setup. Even if you use disposable Qubes, you can’t ensure there’s no evidence of your activity. A better option might be Tails OS or another live-mode OS, especially when used with public Wi-Fi.
Regarding metadata issues with Qubes, I agree there’s no built-in way to hide from your ISP that you’re using Qubes OS. However, you could set up a Whonix gateway before the sys-firewall. Alternatively, you could self-host your own VPN, use anti-DPI tools, and add network obfuscation like Noisy.
I do give the Qubes team credit for allowing a thread discussing the possibility that Qubes is a honeypot (
link). I suspect that, rather than being a full honeypot, Qubes might be monitored, or there may be effective exploits that Western states have access to or at least the willingness and funding to develop when they have a target known to use it.
Qubes is a "security" OS, not an anonymity/amnesiac OS.
Just because you use Qubes doesn’t mean you’re secure. For example, IntelBroker used Qubes for a while, but he got tracked by using the same VPN with his personal YouTube account and sharing a video in the BreachForums shoutbox. The feds correlated the IP with the video, then linked it to his real Coinbase account, which he used to cash out his Bitcoin. The feds even honey-potted him when he sold a database. You can’t make this stuff up. So, while I don’t think the feds need Qubes to be a honeypot, it’s not out of the question.