I've thought a lot about this, as I have only one pack that is big is enough for more than an overnighter, and there's things I like about it and things I don't. I'm not plonking down money on another one, though, until I've sussed out what I really want.
The current (and future) pack:
CURRENT: Lid pocket that is marginally useful. With two safety pins, I can convert it to a summit pack, but I've never actually used it that way, and I have more comfortable dedicated small bags for day hikes.
FUTURE: Would really prefer a rolltop for better weather resistance, with possible removeable straps or a flap to lash something on top. I think McHale makes a flap that doubles as a hydration sleeve, which intrigues me. I love bladders but taking them in and out of my pack to refill is always a bit of a pain.
CURRENT: Mesh side pockets with dual side compression straps. I like size and placement of these but the mesh needs to go.
FUTURE: Solid pockets would snag less and drain holes would take care of water. No change to the straps except maybe to add a third one depending on pack size.
CURRENT: Added my own hip pockets. They are removeable, but not easily.
FUTURE: Hip pockets built for the pack and easily removeable.
CURRENT: wierd, laterally overlapping front pockets with vertical zippers. HATE HATE HATE these.
FUTURE: A simple tall bellow pocket with a velcro top flap.
CURRENT: NO daisy chains or lash points. Why, why, why?
FUTURE: Plenty of well-thought out chains and lash loops.
The kicker is that this pack is very comfortable--I bought it off ebay and totally lucked out on the fit--and I'm reluctant to start accumulating packs based on their features that may not fit as well. I will probably continue using this one until I can afford a custom pack. Probably a McHale. The last time I looked at Dan's site, I saw a number of my sketches were features he already offered on his packs.