The Supreme Magicka plugins are all imported (green text in Wrye Bash) in my load order and all was ghosted except one, the Shivering Isles one is the only one not importable,then apart from merging all to master (SupremeMagicka.esp) I don't see what benefit in therm of soft cap can give that to me...
ALL plugins (excluding ghosted) in your Data folder count toward the soft cap. You may have 250 activated plugins, but all 300 or whatever plugins in your Data folder count toward the soft cap. Merging the SM add-ons would save 5-7 plugin slots.