Post viable alternatives here and your thinking around why.

Being free to leave the iOS ecosystem is the biggest flex anyone can make to enforce beneficial change.

E.G. Signal is the iMessage killer.

What’s your answer around lockdown, security, updates, hardware, iCloud replacement, AirPods etc

I've spent a lot of time thinking about this, as I've long wanted to switch to Android.

If you have an Apple Watch and are using it for anything other than fitness tracking, then you're SOL. Non-Apple alternatives are nowhere near as capable. (In fairness, Apple has done a very good job of making the Watch a useful device on its own and providing a strong app ecosystem for it. I can straight-up leave my phone at home if I'm going to the gym or going somewhere nearby outside of working hours.)

If you don't have a Watch but do have AirPods, then you can switch to Android, but their capabilities will be slightly reduced. (Customizing noise cancelling and transparency mode, as well as add-ons like Live Translation, are only available on iOS.)

If you don't have either of these, then it comes down to apps, iMessage and FaceTime.

Many apps use StoreKit for managing subscriptions. These will need to be cancelled and re-subscribed with Google Play. Apps that were bought outright will need to be repurchased. Several apps (like the Vinegar/Baking Soda Safari extensions, which I, surprisingly, haven't been able to find alternatives for) are also iOS-only, so you'll need to find alternatives or live without them.

Regarding iMessage: you'll need to accept being a green bubble and breaking people's chats. If you use iMessage for most of your communications, this alone might be a dealbreaker. RCS is bridging the gap but isn't all the way there yet, and that's before considering how slowly carriers do things. Good luck getting people to change apps; that's like trying to turn a cruise ship.

FaceTime is really good. Google, despite launching 752 messaging apps in the past, doesn't really have an equivalent that works as well as FaceTime does (to my knowledge). Not an issue if you don't use FaceTime.