> How hard is to convert the UTC time to user's local time and perform quota reset?

Probably roughly as hard as writing a timezone-aware scheduler that considers all edge cases around daylight savings time, i.e. probably possible but I'd try fairly hard to see if I can get around it.

One way of getting around it is to run your batch jobs in your "primary business timezone". Sure, you might outgrow that concept eventually, but many companies never do, and in that sense "running on UTC" seems similarly aspirational in spirit (albeit at a much smaller scale) to starting with high scalability.