Populate optional thumbnails from image blocks in the "Content" pane.
Show Available Pages
To help users see how close they are to running into their subscription's page number limits, there should be a small quota tally at the bottom of the page structure editor.
Two Finger Scroll
In the carousel view of the summary block, there are two left/right arrows on the top right corner (1) used to navigate to the next/previous pages. To improve usability, the carousel block should respond to intuitive horizontal scrollwheel events such as 1) trackpad two-finger scrolls and 2) touch screen single finger scroll events.
Basically, make the carousel block actually behave like a carousel.
On the subject of anchor links (the links that scroll to different positions on the page) I have two (2) suggestions.
1) I'd like to see Squarespace adopt an automatic anchor link system for all header text similar to what's used on Github. When the user hovers their cursor over the header, a "link" icon could appear.
2) my second suggestion