That is a cracking idea to be fair, and if the company allowed staff could work Christmas holidays and take in their specific religious days instead.
Having said that it could be open to abuse, as in that someone could very much go down the current gender issues, that someone could claim to be Christian and muslim or any other religion for that matter and thus maximize their religious holidays.
I could see an uptake on faiths with summer festivals as well
In theory it's a great idea but would cause issues for a lot of places I suspect.......the infrastucture needed to keep places open during what would otherwise be a shut-down (Easter and Christmas for example) would be expensive. If WFH was an option in any particular line of work then it's easier......
I did work with a guy who 'claimed' Jewish holidays but ate bacon sarnies.