The uptake? Like ~30% of the people I'd like to contact bother with it. The rest, it's even worse - we get stuck with SMS. And a lot of conversations I just miss, period, because they're groups of people in one of those other ecosystems (and missing those is a price I'm personally OK with paying, but not everybody will be).
The situation is just really bad. Signal is a good baby step forward, but it's not really the answer for most people, because they're sticky to wherever their network graph of contacts already is, and they're not going to switch just because the one weird nerd in their life isn't available there.