If anyone wishes to comment, the CMA is explicitly wanting those to do so by sending in emails to mobilesms@cma.gov.uk, addressing the questions set out in their report[1], which basically boil down to "Should we investigate apple and google" and then "'what should we do about it"?
Really the main thing that needs to be done is opening up the RCS API on android the same way the SMS API is. Google has been holding on to it to try and pressure people to use their closed source app instead.
[1] https://assets.publishing.service.gov.uk/media/679115f1cf977...