I'd really like to see a greater range of minifig heads, hair and accessories available. Many of these pieces are desireable across lines (Space, Pirates, Castle, Town, etc.). While offering parts specific to each individual builder's
needs is great, often those parts are covetted by a select few builders. I would love to see some of these parts offered in colours unavailable in sets (i.e. the Princess Leia hairpiece in tan). Heck, given the premiums people pay for older figures on bricklink, I wonder why LEGO doesn't run a few of the older popular torsos like the Black Falcons or Forestmen.
I'm going to be very straightforward here; LEGO will have a hard time matching Bricklink for parts prices, however minifigs and minifig accessories are an area which LEGO could easily dominate the market. AFOLs on Bricklink frequently part out sets marking figures up and basic bricks down. LEGO could easily offer older popular torso prints for $1.00 per fig which would beat the majority of bricklink sellers. Consider that the average Black Falcon torso goes for well over $1.00 on Bricklink. Other torsos and accessories sell for considerably more. It's one area that LEGO really seems to be missing out on.
Oh and lots of dark brown.