Why? What mistake? I mean, many people won't use that, but for many it's very handy. And the features delivered with JSONB (e.g. the indexing) is way better than what was available with XML.

Funnily enough I found this Steve Yegge piece from 2004: https://sites.google.com/site/steveyegge2/ten-predictions

Check out the first prediction.

Thanks for the link. Funny indeed. Replace 'XML' with 'JSON' and you have an up-to-date blog snippet.

And sandstorm.io is kinda solving #2

I don't think XML was all that widely used, and the implementation looked more "looks interesting, let's develop something and people will use that".

With JSONB it's more like "people are already using JSON data type (text + validations) a lot, and want something better, and we do have hstore, and we're working on hstore 2.0, so let's use the ideas for json". And that's how JSONB was born.

My estimate is there are already more people using JSONB than XML (talking about the PostgreSQL data types), so the momentum is very different.