This would basically be a way for kids to build up a set of basic blocks in allowance-sized chunks.
Each small bag would contain something like 5 standard bricks and/or flats, one "weird" piece (a wheel brick, a plant, a window, or whatever), and a random minifigure.
Larger bags would have something like 30-50 pieces, with a similar ratio of standard pieces to "weird" pieces, and 2 random minifigures.
Small bags would be $1-2, larger bags would be about $5.
One thing that could be done, both to keep costs down and to provide a potential incentive for less casual buyers, is use these packs to use up any leftover special pieces (or special-colored bricks) from discontinued sets. So, you might occasionally get lucky and end up with something rare. In fact, Lego might want to intentionally seed the packs with a few "rares".
Alternately/additionally, if Lego ends up with any significant number of messed up but still playable pieces (eg misprinted minifigs, bubbles in the plastic, etc--pieces that still lock together and all, but just don't look right), there could be larger "factory second" mystery packs.