I‘m part of the „release iMessage clients on non-Apple hardware“ for years. WhatsApp has pretty much taken over as the new messaging standard in my country and a lot of other countries around the world.People leaving WhatsApp are likely to choose Signal or Telegram which means we may need both apps if our contacts split between the two. With iMessage and possibly WhatsApp for those who stay on WhatApp, we could need four apps! Would be easier if Apple created an Android app for iMessage and then we might not need to have two or more messaging apps.
Apple simply is NO marketshare leader. Android dwarfs them by a great margin around the world. An Apple only texting standard is dead on arrival the second you look at countries where the vast majority of people own Android phones. That‘s why people flocked to cross-platform messengers in the first place.
I feat it‘s a little to late for cross-platform iMessage though and that the great WhatsApp exodus to Signal is nothing more than a blip in the history of messengers. WhatsApp will still be the defacto standard here for the foreseeable future and Signal will slowly fade back to irrelevance again. People like convenience, they‘ll stay on WhatsApp and forget about all the outcry... especially in Europe, where pretty much nothing changes because we have basic human rights here that protect us from a lot of shady practices.