I wanted to echo the comments of many, who like myself have built WordPress sites for clients large and small over the last few years. I have serious concerns, and like Morten has pointed out - there is no one suitable place to express them.

I have embraced meta-boxes big time right from the start, as they offered an extremely flexible way of storing extra information relevant to a page or post, or any custom post type that I cared to define.

Some of the information in the meta boxes will ultimately appear on screen when someone visits a site, but it may appear in different ways depending on the context. Other meta data can just be used for deciding which posts to show in a given WP_query, or even for sorting too - although I know that's perhaps not the most efficient use. But WP_query has params to support that - so it's obviously not just me...

My sense of foreboding and concern comes from what happens when WP version 5 with Gutenberg is released. From what I've gleaned from the diverse sources of information and gossip, I wouldn't be surprised if pretty much all the sites I've built will either break or stop being maintainable, without some serious amount of redevelopment work.

This will create a lot of pain for the small businesses and charities I've built sites for. Even though I no longer have them as clients any more, they will probably approach me to express their frustration. Even more so when they hear that substantial rework of their site may be required - they, and I, will wonder just who is supposed to pay for that.

I want to think that the Gutenberg team will deliver a great editor when it's all finished, and I'm sure it will make building new sites easier. But please, don't overlook all the existing WP sites.

Maybe we need a central repository where people can share all the different ways they use meta-data, and where the Gutenberg team can understand how they need to accommodate those different ways.