Date relative to another field

Currently in the formula filters, dates can be defined as relative to another date, such as the image shows below:

However, what I'd like to be able to do (and would make my data updates a lot easier) is to make the the "6/28/2015" field above another field value (not just a static date).

Another date request: I would like to be able to query an object's child data and find out the max or min date.

I am encountering the same problem as above user. It is necessary to make sure the user will not enter a project closing date earlier than the project start date, and for every task detail dates as well. Please add this feature ASAP, thanks!