As of January 14, 2020 -- the date when Microsoft is slated to stop providing support (via patches/security updates) for Windows 7 with Service Pack 1 -- Microsoft will no longer support Office 365 ProPlus on Windows 7. That makes sense. The company already is not providing updates for ProPlus running on any Windows 10 Semi-Annual Channel versions that are no longer in support, which also seems understandable.
However, Microsoft will no longer support Office 365 ProPlus on Windows 8.1, Windows Server 2016 and older and any Windows 10 Long Term Servicing Channel (LTSC), as of January 14, 2020. This is despite the fact that Windows 8.1 will continue to be supported and patched by Microsoft until January 10, 2023. Windows Server 2016 is still in support until January 11, 2027.
Office 365 ProPlus, which is available via subscription licensing only, comes with Outlook, Word, Excel, PowerPoint, OneNote, Access, Publisher, Skype for Business, OneDrive for Business, and the Office mobile apps.
Microsoft's argument is that these coming restrictions will "ensure that both Office and Windows receive regular, coordinated updates to provide the most secure environment with the latest capabilities."
For those use Remote Desktop and VDI/desktop virtualization to make Office available, Microsoft is planning to deliver updated virtualization capabilities in its Semi-Annual Channel releases of Windows 10 Enterprise and Windows Server -- which means this fall with 1809, I'd assume.
What about Office 2019, the next non-subscription/perpetual version of Office?
At Ignite, Microsoft announced Office 2019 would be available in calendar 2018, with a preview coming by mid-year. Today, Microsoft reiterated that plan, officially stating Office 2019 will ship in the second half of calendar 2018, with previews of the new client apps (Word, Excel, PowerPoint, Outlook and Skype for Business) and servers (Exchange, SharePoint, Skype for Business) coming in the second quarter of this year.
Today, February 1, we learned that Microsoft is only going to support Office 2019 on Windows 10 -- not on Windows 7 or 8.1. The Office 2019 apps will be supported on any Windows 10 Semi-Annual Channel release that's in active support; Windows 10 Enterprise Long Term Servicing Channel 2018 (which will be out around October this year) and the next LTSC release of Windows Server.
The Office 2019 client apps also will be released as Click-to-Run only. Microsoft won't be providing a MSI option for Office 2019 clients, but will continue to do so for Office Server products.
Microsoft also is cutting back on how long it will support the next perpetual version of Office. Instead of providing five years of mainstream and five years of extended support for Office 2019, Microsoft is going to provide five years of mainstream support and approximately two years of extended support so as to align with the extended-support end date for Office 2016 (which is October 14, 2025).
Microsoft officials have not said if there will be another perpetual version of Office after 2019; they continue to say they'll monitor customer feedback before deciding.