“…instead of unnecessarily burdening all the present plugins with unsolicited notifications (for most of them), it would be better if plugins that want something like this, actively request (registered somehow?) that info being sent only to them by the N++.”
Indeed, it (adding a new API) will be the better solution than keeping all events of SCN_MODIFIED notification ON for some plugins which don’t need the all these events, or even for users WITHOUT any plugin.
In the worst case, users get all the plugins which need ALL the events of notification SCN_MODIFIED and the performance will be equal as the old configuration (v8.7.5 and former versions), not worse.
But in the most cases, the performance will always be better than before.