Well yeah, because it means that I just message a contact in my default messaging app, and if they use Signal it goes over Signal, and if they don't it falls ba

Well yeah, because it means that I just message a contact in my default messaging app, and if they use Signal it goes over Signal, and if they don't it falls back to SMS (just like the experience of the system messenger and iMessage on Apple devices). But you're right - what we really need is a way for each messaging app you install to be able to inform the system which contacts it can reach, a simple way to set a priority order (eg. just a draggable list where you can put iMessage above Signal above WhatsApp above SMS), and a single messaging frontend which can render all the ongoing conversations in each installed messenger. (I believe AppleTV attempts something like this for video streaming services?)