I still plan on holding onto 7 as long as I can. I still have yet to hear anything positive about 10.
I've used Windows 10 on all kinds of hardware from new to 10 year-old desktops and all run as well or better than Windows 7. Keep in mind, it's always wise to do a full backup and then a clean install.
One of the biggest reasons to hang on to Windows 7, is if you need Windows Media Center (which isn't in Windows 10), otherwise upgrading is a wise move for most users.
This article may be helpful:
Microsoft's much-hyped free upgrade offer for Windows 10 ended years ago, but it took more than seven years before the company finally updated its activation servers. Here's what upgraders can expect now.
www.zdnet.com
On the other hand, I have heard that apparently 12 (no 11) is in development right now.
Windows 11 is not in active development. When Windows 10 was released in July 2015, Microsoft said that Windows 10 is the last version of Windows as they began releasing semi-annual feature updates.
However, since then Microsoft has said that Windows 10 support will end in October 2025. So we'll see. Regardless, that's more than five years from now. A lot of hardware won't make it until then.
Hope it helps.