Out of curiosity, why SHA-256? I would wager using a non-cryptographic hash would be faster, no? In this context you don't need any of the crypto properties of it, so that could be an easy performance improvement for your cache.

It seems currently the scroll struggles when you jump around, e.g. when you click to the bottom of the scroll bar area, the scroll will jump twice, first as you click and the second time as it renders. This is not a big issue if you continuously scroll, but is very noticeable if you use page down or click on the scroll bar. At least on my system, there is a noticeable delay between scrolling and the items being rendered on screen, that might be a related issue?

Those notes aside, I could definitely see value for this in cases when you want to get a glance overview or similar of a large number of notes, it's a cool idea.