Is it possible and would it be a 'supported customization' to create a Lookup field towards Calendar Entity on any other entity?

I need to create lookup fields towards the Calendar entity in order to track working hours against some other custom and system entities.

This should be used exactly the same as it is on the System User entity, Resource Entity, Service entity, or the new Bookable Resource and similar entities.

Through the CRM Customization UI this is not possible, and the Calendar entity is not available through customization part of CRM.

I have not tried yet to create a field through code, but even if it is possible, i would like an opinion, if this would be a 'valid' CRM customization.

Thanks.