This works if you can switch out The design as in the old "napkin look&feel" for Swing.[0]
Sadly I think "change design by switching out a theme" has long died as an idea in the web space.
The issue with "theming to look sketched" is the same as with "hand drawn looking components" - it has to be integrated for your specific DOM or App, totally defying the purpose of "making someone understand this is a quick sketch". Because by now, it's far beyond being a sketch.
Consider building a calendar app. You build part of the thing, but you have not handled error conditions and edge cases, the back-end supports only a single user and you don't have authentication working.
It's enough to validate some of the flows and how UX actually works, but if you show it to a customer with the actual proper designs they will subconsciously asume that the work is finished.
If the look and feel is "this is not real" it sets their mind in a different configuration.