We should drop support for multiple cache groups as it have little practical sense.
Only available caching provider with proper support for it is OS Cache and it is obsolete and should be actually deprecated too.
So here is required API changes:
- replace internally multiple cache groups with single group
- deprecate corresponding 3.1 API and warn when multiple cache groups provided
- remove corresponding 4.0 API completely (e.g. in fluent queries API)