The end of the Cubase API for plugins will arrive when Steinberg will decide… and since Cubase has a larger user base, VST3 will surely be supported for a long time.
CLAP supports per notes expression…so does VST3. the « temporary modulation » can be implemented in a DAW with no specific support of VST. One interesting thing could be the enumeration of plugin metadata without loading the plugin. But I have no issue with VST3 (VST2 enumeration is slower).