I'll try to explain me.
In fill tool you can double click over the arrow and add more colors to the fill and get several color effects.
I'd like to have the same utility but in transparencie tool, that is to say, you choose the transparencie tool, drag, double click over the transparency arrow and set the value of transparencie for that point, I could get diferent values of transparencies for every point in the same way I get different colors when I place points over fill tool.

Other:

Today you can apply a flat, circular, conical, etc types of transparencies, but you don have a transparencie that match with your shape, if you want to apply a transparency following your shape you can't or I don't know how to do it, today I use feather, but it is not the same, do you understand what I mean?.


Other:
Idem to fill tool, I've needed more than one time to be able to fill a shape with 2 or more colors following the form of the shape, to get that I have to use for instance contour + feathering or transparency to get the result.
I think that have a shape fill (as we have, conical, circular, eliptical, etc) would be great.
I hope you be able to understand my explanation, it is a bit difficult to me to explain.
If you need more detail I can make some drawings to explain me better.