Thought it might be interesting for you all to see what this debate looks like from the other side of the fence - these guys have a piano roll, and want a tracker interface added 
http://forum.cockos.com/showthread.php?t=14303
By the speed reaper comes with updates it will be faster integrated as a piano roll in renoise 
hehe … hope this will speed up things … 
I use reaper quite a lot, and it’s totally unnecessary to have a tracker built in, i’d be more worried about getting a better piano roll and midi sequencing to begin with.
IF i need to use a tracker in reaper, i either run renoise in it or ReVisiT. Revisit is really all you need.