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Nothing Phone builds a blue bubble iMessage bridge while Google and Apple fight over RCS
(www.androidcentral.com)
This is a most excellent place for technology news and articles.
The limitation was added after the fact anyway, like I mentioned in my edit, secure enclave wasn't added until the A7 chip, which was first used in the iPhone 5S in 2013, two years after iMessage became available.
It's really not necessary though, it's just a justification after the fact. There are several secure e2e apps available without utilizing a special chip to house that data, even Google has e2e with their RCS implementation