Support RegistrationType "ContentType" in Command Set Extensions
This suggestion stems from a discussion held in the SP Dev Docs at https://github.com/SharePoint/sp-dev-docs/issues/871. Documentation has indicated support of setting the RegistrationType to "ContentType" in a Command Set Extension. However, this setting is not actually supported (as mentioned in the closing comment on the issue). We feel this setting is quite important and should be supported by Command Set Extensions. Without this setting, your only option is to target a List Template (RegistrationType="List"). This is very problematic when you are attempting to target the Command Set Extension to a specific list or even multiple lists with specific content types. As a workaround, I ended up writing very specific conditions into the code so the Command Set Extension wouldn't do anything and would be hidden on lists based on the same list template. This specificity makes my Command Set Extension non-reusable.
I agree with this suggestion unless another mechanism is in the works. Seems like unnecessary bloat to have a command set deployed to all Lists or all Libraries. Then have it figure out if it should show or hide. Wasted compute cycles that can drag performance.