I think to get a wider adoption CP needs to be compatible with existing plugins and themes.Maybe somehow keep methods consistent and/or do regular partial merges with WP core.
As I consider options in response to the WP-Gut thing, the first question that popped into my mind re ClassicPress dealt with plugins. I prefer to write my own functions but there are times when best use of time makes it foolish to not opt for a well-written and supported plug-in. That said, I continue to prefer "The Drupal Way" of providing high-powered tools (modules) that can be used to build extensible and scalable sites rather than solutions in the form of plug-ins.
@Sunshiney, I'm unclear on the difference between modules and plugins, as you've described it. Can you elaborate on what functionality a module provides?
ClassicPress is, and will continue to be, compatible with any WP plugins and themes that work in WP 4.9.x.
Any major plugin will need to keep compatibility with WP 4.9.x, so I think there is nothing else for us to do here.
For more details, see: https://forums.classicpress.net/t/longevity-for-cp/180/17