on tumblr you have full control over the HTML of your page, but posts must conform to a particularly strict subset of markup
here, you have deep control over the content of each post, but limited control over the appearance of the rest of your page
page customisation does seem like it’s on the roadmap, but it’s interesting how it highlights the difference for me; the HTML-powered creativity and expressiveness isn’t limited to when you, on occasion, click off the timeline, it’s embedded directly in it