I notice a lot of OEM PCs, for example, come with an Office 365 trial install. I'm sure the OEM deal is "Windows is 30 cents cheaper if you include the trial."
But if the OEM is already installing Ubuntu or whatever, they 1) no longer need to negotiate to shave pennies off the Windows license and 2) have an office suite pre-installed, potentially capturing a large number of the easy customers who'd click on the first thing available.
How does Microsoft keep that sales channel open?
I can't imagine them going the road of the shovelware antivirus vendors and outright paying OEMs for presence. But I could see them packaging up a cut down "Linux Subservices for Windows" product. This would be basically a blessed virtual machine package, which OEMs would be willing to include-- or maybe even pay a token sum for-- because, well, people still want to run their games and legacy software. More importantly, it's a way to get millions of people to install a MS-provided package on their desktops, which could include cross-promotional offers and telemetry. (Yes, there will be the inevitable shut-up packages from third parties, but they have those for Windows already).