As identified by @ppmt in #6, having wrong date format in the include/exclude dates will cause Home Assistant not to start. A fellow developer discovered, that this happens if you add the dates without quotes.
If you use include/exclude dates, please make sure you include them within quotes (see the documentation).
Dates without quotes work fine if the date is valid, but an invalid date will cause Home Assistant not to start.
I think this is a general bug, I am addressing that. Validation of dates embedded in quotes works fine.