not sure i can, in good conscience, request these, since they are so pie-in-the-sky, but...
1: will attachments be able to know or find their locations in world space?
2: will other avatars be able to sit on attachments?
1: if you look at jousting in second life... it is a huge pain to figure out if your lance tip hits something, since the lance can't find out where its tip is, in relation to the world at large.
lance builders/scripters had to put the lance on an avatar, put it in the animation, then basically guess where the lance tip was, spawn a bullet in the world at that location... see if it came out anywhere near the lance tip... adjust coordinates... and that was just for one lance position. (on one sized avatar.)
when i was a noob, i tried putting a sensor sphere around the tip of the lance and checking if it hit anything. HAHHA! ;) dopey me!
actually, come to think of it... if an attached sensor can sense where it is in the world at large... that would be a huge step.
2: yes, sitting on an attachment. that, like in #1, knows where it is so it knows where to put the sitting avatar? so the avatar's butt can stay connected to the other avatar (get your minds out of the gutter!!).
like a saddle on a horse (or dinosaur... or dragon.. etc!) avatar. or i can wear a glove and my falcon avatar buddy can perch on my arm. or my shoulder.
or people can carry other people. or walk hand in hand. push a baby in a stroller. or whatever.
if we're going to have to rely on vehicles that two(+) people need to sit on... can there be some sort of... built in avatar-movement simulator thing? because building a physical vehicle (or non-physical one, even) that walks, runs, jumps, flies, and everything else exactly like an avatar does was a REAL PAIN in second life.