Apple's iMessage allows iOS and macOS users to send each other end-to-end encrypted messages. However, this is different if the message is sent from Android to iOS or vice versa, where the message is sent only as plain text which means it is not safe enough during transmission. This is what will change.
Google also wants to change things, in his tweet on Twitter Google Android SVP Hiroshi Lockheimer hinted for Apple to adopt the Rich Communication Services (RCS) protocol.
The RC protocol was designed as a replacement for traditional SMS. It's also supposed to be a platform-agnostic alternative to other messaging apps like Facebook Messenger, WhatsApp, and iMessage.
Currently the service requires users to have an iPhone or register for a Facebook/WhatsApp account. This service can be compared to SMS where as long as the user has a cell phone, phone number, and cellular connection, the user can send and receive SMS right out of the box.
Google has been pushing the RCS protocol for a while now. So far the major carriers in the US have agreed to adopt it.
Apple is one of the few major tech companies to survive, but that's not surprising because iMessage can be an incentive for users to buy Apple products and use its ecosystem.
