Hi @Zvi_Twersky,
There’s already a Product Feedback topic for having “users” as a type of dropdown custom field; you can vote for it here:
I agree having a users custom field type would be very useful.
I think the argument for having a similar one for tags is not so strong; first, why would you need a custom field when you can just tag the task itself; and second, unlike users it would probably require having a multi-select capability. What’s your use case for needing a custom field dropdown with tags in it? I’m open to being convinced… 