Hi,
I also met this situatation then I updated my powerbi-visual-tools to 1.2.0. checked the schema.capabilities.json file. yes it abstracts the drilldown capabilities.
So I enabled drilldown in capabilities.json like
"drilldown": {
Roles : [ "Category" ]
}
thats it . my custom visual enabled with drilldown :-)
I hope this will help you.
Thank you,
Balachandar Gopal