For Microsoft, shifting to universal apps was a way to shed legacy baggage and encourage support for post-PC devices. For Google, bringing Android apps to Chrome let them tap into native functionality and performance.
For Apple, it lets the massive iOS platform help pull the Mac platform forward.
If true, this would be another classic case of Apple copying an idea where that others have failed to execute.
It's a brilliant idea but the success or failure of this type of move would come down to the nitty gritty details that will affect iOS/macOS developers.