What I would personally do in a situation like that is to make two topics and link them. Adding a search box is a feature suggestion that can live separately from the issue with the sub-notebook display problem (which is what you originally did). For example the latter problem could in theory be partially solved by allowing horizontal scrolling when it overflows like that and I'd even say it could probably be logged as a bug directly onto GitHub instead. Having two different issues like that in a single topic can get rather confusing and can steer the conversation to or away from either one.
For the record you already had somebody particularly influential in Joplin development commenting on your topic (look at the top contributors to Joplin - Contributors to laurent22/joplin ยท GitHub). This is what I mean by not needing to target people with the blue Joplin icon, your voice is plently loud enough just posting a topic, there is literally no need to PM or ping people when the topic is already getting attention from the right crowd.