At the moment, during import roon picks up an albumart using his own criteria.
i’d much more prefer the possibility to specify a user specific filename (cover, albumart, front, etc) to look for.
This should be possible. Look in Settings->Library->Import Settings. There Artwork source is selectable
That’s there but roon seems to pick up just the first embedded artwork it finds in a file. If more than one image is present it’s lost on roon. Like if you have a cover (front) and cover (back) embedded - roon will ignore the second one. At least extracting those images from the files would be nice. And/or giving preference to Cover (front) images.
I have not tried this with more than one cover art image so I would not know unfortunately. There may be a difference in embedded vs separate files. Under Settings->General there is a ‘Allow for more covers and photos?’, but I do not know if this affects the cover art logic. Sounds like a bug to me…
I couldn’t figure out what “allow for more covers” is supposed to do but since “more” is often better I had switched on already. 
Well, it probably works as built - take the first picture found in a file and use it. Everything beyond that might be an enhancement. A bug would be better: that would have to get fixed … 
I’ll wait ('cause I think I like roon, anyway) …