Most people have decided to make their platform streams their digital gardens, and within the confines of a story card, they're largely free to combine whichever content they want. For a decentralised, self hosted solution to make sense for them, that solution would have to solve market reach and interactivity problems before it should think about canvas issues. Actually, for most "daily blogging" people are fine with facebook's title-less box, and even for much of longform blogging market/connectivity issues have led many people to move to Medium, which is basically a single theme for everyone.

Basically, I'm not sure WP isn't trying to solve the wrong issue first for those customers who are intersted in that kind of recreational gardening. It's like giving them the tools for (learning to) gardening without giving them the real estate to do it with.

"It may be a rough ride for some agencies and businesses around the platform, but I am OK with that. They will manage and pull through on the other side, mostly unscathed."

That would imply business customers stick to the platform in the long term, which I'm not sure about. Market share and people used to working with the
WP are clearly an important asset. WP.org sites are, if I'm not mistaken, mostly powering small business sites world-wide, which don't care their employees gardening needs.

So the question will be to which extent a single product can support the gardening needs it may consider its digital heritage and future (like you suggest) and the requirements of those currently mostly using the product.

It was a bold strategic decision that's for sure, and I've spent so much time with WP since about 1.5 that I hope the platform will continue to thrive. But I'm less sure than in a long time, despite the market share and power.