Although I don't like fixing browser quirks in Unpoly, I'm thinking about changing the default event blur for date inputs.

Agree it's not up to Unpoly to fix browser quirks - especially as there is a workaround by using a simple compiler. Also, if you only change date/time/datetime inputs to listen for blur rather than change, it may be a little jarring and inconsistent when other inputs only trigger validation if the user actually interacts with the field?

In my case, I prefer the validation to occur on blur for all form fields, so there is immediate feedback if a user ignores a required field. In which case the compiler is required anyway which negates the date field issue entirely.