We may go next year to cleanup a bit. That may include moving some classes/functions to use functionality from Windows 8/8.1, so the minimum for those plugins will be that version. If you need Windows 7, you may then be required to keep older plugin versions. Also we may want to move to use more Visual Studio 2019 features, so some plugin parts may start to require the newer runtimes. Not a quick change, but more part by part, where we see benefits. And of course you could always use an older plugin for some special project running on old hardware.
On macOS we'd like to get rid of Addressbook framework. You may need to move to newer functionality provided by Contacts framework. If needed, we may add more functions for Contacts in the plugin. Let us know what you miss to make the change.
For Linux, we may ditch GTK 2 and link directly to GTK version 3. This can simplify some coding for me and since Xojo uses GTK 3 exclusively for years, it shouldn't cause trouble for developers.
Let us know if you have questions.