I think iMessage's ship has sailed. WhatsApp appears to be ubiquitous now, even despite the privacy concerns. There's no way I could set up any sort of group chat in any other app. Having a platform-specific chat app was always going to lose in the end. Even iTunes/Apple Music has a Windows version.
I personally avoid iMessage and FaceTime even with other Apple users, because I have found it impossible to figure out the correct settings / contacts-setup to avoid messages getting lost between SMS or iMessages, and to get the same contacts synced on each of my Apple devices, despite being signed into the same Apple ID on all of them.
I personally avoid iMessage and FaceTime even with other Apple users, because I have found it impossible to figure out the correct settings / contacts-setup to avoid messages getting lost between SMS or iMessages, and to get the same contacts synced on each of my Apple devices, despite being signed into the same Apple ID on all of them.