Yes, true, per-contact notifications "slipped through the cracks" - it's one of the (many many many) "ideas for future versions", but hasn't been picked up for dev.
Maybe you could help us understand what *your* expectations from this are?
I can see at least two -- opposite -- scenarios:
1 - "When I get home from work, I put the phone into silent mode, but my boss / mom / girlfriend are on the priority list, so I want to be notified with a sound"
2 - "I went to see a move and put the phone into silent mode, and then stupid Aqua Mail played a sound when there was an email from my wife"
Comments, ideas?