The Piano Roll needs an easy way of importing midi.
Drag n drop would be good, but if that's too hard maybe you could have a DROP IN point at the top of the Piano Roll that you drag the midi file/loop onto that will import and merge/overwrite (option) to the cursor position using the existing routines.
This will make things a lot easier especially creating the custom drum track you need, how it is now you have to import a midi file into one track then copy and paste the bars you need out of it to the drum track.

If I try to Drag n Drop I get this forbidden symbol:
EDIT: Same deal when I try to drag drum audio loops into the Audio Edit window "forbidden symbol"

Yes, definitely a worthwhile feature.
+1

+1

+1
but for all the MIDI tracks, there is no reason to restrict this feature to the Drums track only.

+1 Don't limit the feature to just drums.

<<< "This will make things a lot easier especially creating the custom drum track you need, how it is now you have to import a midi file into one track then copy and paste the bars you need out of it to the drum track." >>>

It is easy to import a single track into BIAB and open the Piano Roll to edit it using either the Melody or Soloist tracks.

Here's what I do (I'll use the Melody Track in my example.)

Open Biab
From the top Menu Bar Select Melody\Track Type (Multi(16)-Channel)
Melody\Edit Melody Track\Import Melody from MIDI File
An Open Dialog Window opens
Navigate to the MIDI file you want to use and select it
When the import MIDI window opens, select only the Channel you want to import and be sure all of the other channels are deselected. (Drums are usually channel 10)
The selected channel will be imported to the Melody Channel
Open the Piano Roll and select the Melody channel for editing.

EDIT: "+1 Don't limit the feature to just drums."

Any instrument or channel can be imported in this manner, not just drums.

Repeat these steps using the Soloist Track to import a 2nd MIDI track, from the original file you are using or a different file altogether. Import two tracks for instance to have complimentary drums and bass for your song.

There's nothing about drums only the drums were just an example, drag import will work on all the midi tracks.
You may be using a pg midi drums track but want to enhance it bit so you just drag a drum solo/fill/roll in at whatever bar you need and it will overwrite the existing midi or merge with it.
Like if you are using free MT Power Drummer or free DrumMicA you can drag the midi drum section out and into the piano roll.
http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=459905#Post459905