When I was testing, the collector was a great boss. Well designed, great attacks, pretty much everything that is in a great boss.
I would like to see more of him.
An idea would be that there are prestige missions about him that would be added into the rotation.
Another one would be have him spawn randomly in random levels.
The last one is buildup. You hear nothing about him until the mission, how about when you're on the BS testing levels, you could see shadows of him flying by like that one boss in super metroid. It would provide some great buildup and get the player to have this feeling of being watched...
I think that he can take place in one of tortodrone levels. Also he need few stages, i can kill him instantly with 5* brandish charge and miss few monsters.