Basically, every plugin is mono. It processes “a” audio channel. A stereo plugin is actually two mono plugins with linked parameters. A VST3 plugin is a -as many channels as needed- multi mono plugin.
What has been asked for is a x-number of plugins side by side with the possibility of linking some parameters.
These are multichannel plugins with their own specific problems.
Mostly the are fixed to a specific channel config, and not usable within another config.
Which basically comes down to the fact that each and every user wants/needs a different set of plugin configurations.
Fredo