Custom expression with multiple functions

I am unable to use multiple functions while building a custom expression.

Something like Average(Count(Distinct("Column Name"))) is currently not possible.

Is this not supported at the moment or am I doing something wrong?

Nested aggregations like these are not currently possible. You can, however, do mathematical expressions which include aggregations, like:

(Average("X") - Count("Y"))*100

Any plans to support such features in near future?