OK, got an answer.
It seems to not be on the feature list and roadmap any more - it was initiated in 2016, 3 years ago.
I need a replacement for a very good Password Manager that will not be maintained any more; that is why a custom import template is necessary. Enpass is great for starting a new Database, but not usable for many other that need importing. Sadly, I used none of the listed databases under import, and the pre-formatted csv files are very restrictive. If only the custom templates could be exported as the pre-formatted CSV's, and then be imported with the custom templates.
So, I will have to look elsewhere for import support; pity ... it seems so promising to have custom templates, but unfortunately no import possibilities with them.
Ref.: