> However, the moment they officially acknowledge Linux support, then it becomes a support surface.

Apple documents lots of things the genius bar won't help with. For example, Apple provides instructions for compiling custom builds of the XNU kernel. However, if you replace the stock kernel and your Mac kernel panics, the genius bar isn't going to help you. (Maybe they'd help you wipe the computer and restore everything to stock, but I imagine they'd do that if a Linux user walked in too, even today.)

I suspect Apple hasn't shared documentation because it would take time to prepare for external release (legal stuff, plus the need to avoid leaking future products). What I don't understand is why Apple hasn't made an engineer available to talk on the phone for a couple of hours a month. This would amount to a rounding error in their budget.