@nm In SageMath you can. So, generalizing "..there is no such thing, and there will never be such thing in CAS." is a very unfortunate statement.
You can input a 1st order differential equation as
and it is a very valid statement. For me, It really doesn't matter how internally a CAS represents this. SageMath represents it as the following before it is sent to desolve
The bottom line is I shouldn't have to be forced to enter a differential equation in the derivative form. The differential form of a 1st order differential equation is a very common form one can see in any text book and I don't see why it shouldn't be in any CAS let alone Maple.