>he implication of imprecision in the underlying data through rough looking "hand drawn" charts and graphs is a really smart design hack.

The same approach could be used for mockup apps/websites

If you haven't tried this, you should. The type of feedback you get is proportional to the fidelity of your mock up.

Do a high-fidelity, fully realized html mockup, and you're more likely to get feedback about the little details like fonts, colors, icons, spacing, wording and maybe minor tweaks to the layout.

Draw a really low-fidelity mockup with a sharpie or on a whiteboard, and you're more likely to have a good discussion about fundamental layout/concepts, overall approach, etc, without anyone getting hung up bike-shedding about the details.

I think a lot of this has to do with perceived effort: if people think you spent hours building it, they're less likely to suggest a change that would throw most/all of your work out. This doesn't mean you can't or shouldn't prepare ideas/drafts beforehand if you want to, nor that you shouldn't increase the fidelity as you iterate.

I've tried many tools for this, but personally all the best and most fulfilling [early] design discussions I've ever had involved standing around a whiteboard.

I use https://balsamiq.com/ for this.

That was my first thought when seeing this... IIRC, XAML had a similar rendering option as well.

It had, in Expression (Blend?) but not every component had a draw-like component which made things a bit awkward. Or maybe I missed something. Anyway XAML is still my favorite UI platform, it’s sad Microsoft doesn’t make any effort to make it cross platform.

Well, XAML itself doesn't have anything to do with UI, it's just a serialization of an object graph with hints about code generation.

There's AvaloniaUI, though, if you're looking for XAML, UI, and cross-platform.

At the risk of self promotion, I made something very much like this a few months back: https://anvil.works/blog/xkcd-style-apps

It was inspired by the 'xkcd' matplotlib theme, which itself is delightful: https://matplotlib.org/xkcd/examples/showcase/xkcd.html

There is actually a java swing look and feel called napkin from over a decade ago that is similar.

http://napkinlaf.sourceforge.net/ has some pictures. It's actually good for mockups, since users don't assume the feature is done when they see it.