I had/have this 'I don't want to see any .nef files around and also no
stupid videos' - problem and I was browsing around and had a closer
(?) look at the 'media types'.

There has been discussion earlier about raw files but as far as I
remember, a real solution has not been found (the implementation is
not the thing here, I'd just like to know that a good solution exist).

So:
1) How about making the 'media type' - category similar to others in
that sense that you can create categories and sub-categories yourself
but the difference would be that it automatically selects the files
that belong to each category. If the user could decide the file types
to select in each category, this would extend the usage of KPA over
it's limits now and also solve some existing challanges (like my .nef
- problem ;)

The ultimate goal of this all would allow managing (archive) any file
types with KPA.  Now we have photos and videos.

How about extending to audio files? No, I don't mean MP3 tag
management (unless someone wants to implement it of course) but
tagging the files for example the radio programs you've recorded or
created. Interviews, speeches, whatever. Location, person, keywords,
date..

How about program files, your .py or .java scripts and programs?
How about OpenOffice documents?
How about (you name it)..?

Of course KPA doesn't have to be able to show all this but recognize
and be able to open the file in the (KDE)-associated program.

So an option to accept any file types (and ignore the rest) to a user
specified category.

The idea with Media Type subcategories:

video,
video - ogg,
video - mp4

photo
photo - raw
photo - jpeg

audio
audio - mp3
audio - ogg

and a filter to create these.

Being able to archive all your media in one program would sound great.

2) Personally I think that KPA core function is archiving, this means
adding, tagging finding and watching. I myself find KIPI plugins
pretty useless. I prefer doing things with programs that can do it
best: Manage my archive with KPA, manipulate the image with Gimp and
create a photo gallery with my own scripts.

I'm kind of trying to say that concentrating at what KPA does best and
removing some limits would possibly make KPA even more popular. I
don't know for sure, of course.