Personally if they ever did go sub I'll probably go Linux for good and do all my gaming on a console,never thought I would say that.
Consoles have subscriptions too... Either Playstation Plus for "free games" periodically, or Xbox Live for multiplayer experiences and interactions. The only one without one, is Nintendo.
And they are more expensive than a Office 365 subscription... per user that is.
I wouldn't want an OS subscription anyways - for stationary desktop PCs, and would continue to support a fixed pricing, periodic release every few or several years for upgrades to keep some machines up and running. With laptops and Tablet PCs, it depends but they generally last through at least a majority of an OS's time line before I change hardware itself, or I may overlap in two OS versions before a change in laptop/tablet PC.
Also, either way, if it is a change to the subscription model, it would also partly be on Microsoft's end AS WELL AS the OEM's end for support. Right now, it is entirely under the OEM for end user device support, with Microsoft catering through OEMs for major workings. Reason why you don't here it from this very forum, is that when each of us bought OEM copies, we assume we are the support in entirely, and thus handle such accordingly. If there was a problem, those very people SHOULD collaborate on Technet and MSDN for feedback and collaborations to the fixes.
The above paragraph is a reason why I do not mind sending in error reports and logs to assist in the process.
Come think of it, I have NEVER upgraded a personal laptop's OS throughout my ownership of one. My Inspiron 6000 still has XP on it, the Envy 14 last I parted with it still had 7 as the time I bought it.
On the other hand, most of my desktop PCs through their hardware active lifetime always had at least one OS change on them. XP to 7 on one, 7 to 8/8.1 on two of them.
The only exception is back in the days of the Athlon and Athlon XP days where I changed from 98 to 2000 to XP.