[BizarroLand]

The only thing I can think of as a negative is that it raises the bar for new players to join.

You already will have a very tough time hosting your own materials without using a major player as an intermediary. Emails in particular are far more likely to be blacklisted simply because they're not originating from a known approved source regardless of your DKIM, SPF, or DMARC settings. Adding that every new website has to be fully accessible to the visually impaired when on top of that there isn't a single collectively approved standard to measure yourself against would be an enormous hassle and stop a lot of new people from even being able to take a chance with starting a new website.

However, that is remediable with an approved standard to meet and clear guidelines on the processes that must be followed to meet them, so that's not as big of a deal as it can be made out to be.