I've seen a lot of ideas (example, this one: https://communities.bmc.com/ideas/3716) which request additional functionality. I think a lot of these ideas can essentially be grouped into a more powerful single field type. In BMC SDE, this field type was called a 'Calculated Field'. It allowed you to write your own SQL query and it would return the results within the field. The query would run (and results returned) upon form load, and on save.
I believe a field of this nature should be implemented in FP12. It has so many possibilities.
In the example from the idea above, they want to calculate the time difference between two fields. A great idea. But how do you display the results? Days, hours minutes? Hours? Minutes? Another method. Is it numeric or text. Obviously BMC cannot easily account for everyone's desired output. SDE's 'Calculated Field' would be able to as you'd be able to define your return format within the SQL string.
[Edit on 26-Sep-19]
The following ideas could be accomplished by this idea:
On-screen date range, or blackout validation (Only partially, the blocking of the save cannot be achieved without this idea: XXXXX)
Date fields - validation, automatic populating... (In combination with an on screen rule using the calculated field as criteria)
Allow appointments only for the future (similar to the blackout validating, we could use a calculated field to trigger a notification, but the blocking would be required again here)
ENH: A way for business rules to compare two custom date/time fields as an issue criteria (the calculated field would do the comparison and the business rule would run based on the result)
ENH - FP 12 - add the ability to compare two fields in the criteria of a business rule (Again using the calculated field to do the comparison and the rule triggers on the result. However I would still want this idea to be brought out as it's own as it is quite important.)
There were others in the past but those ideas were declined.