I think the new concept art is a step in the right direction. These proportions are closer to real-life little people, which gives the halflings more of a "Willow" look (for obvious reasons). I'm not sold on this approach, but it doesn't bother me in the same way that the previous concept art did.
At the same time, it looks like the art is trying to do a little too much with the body proportions. Yes, they are an indication of size, but showing other objects for scale is also hugely effective. Lidda didn't look wrong because she was generally depicted in context that made her size evidence. Yeah sure, depending on showing scale by comparison limits the range of possible art, but is it really that limiting? Shouldn't most D&D art have some scale-providing context anyway?
I would try to create a list of objects that halflings tend to carry that help show their scale, mostly objects that are either found in nature or would be traded from a human-sized communities. Fruit (like apples), feathers, animals or animal skins (a squirrel skin cap or waterskin? a dog or goat pack animal? just about any familiar?), human/dwarf-scale buttons, buckles, knives, vehicles or weapons -- any of these can help show scale. Objects can also be repurposed -- a human ring can be a halfling broach; a human cane can be a halfling staff; a human teacup can be a halfling tankard; a human shirt can be a halfling cloak; an elven vest can be a halfling robe; a dwarven hatchet can be a halfling battleaxe.
These objects are important not just because they show scale, but also because they show how halflings interact with the gameworld. That kind of detail kickstarts player imaginations, and isn't that the real purpose of D&D art anyway?
(For what it's worth, I thought the first set of concept art did a pretty good job at using scaling objects in interesting ways. This second round isn't as successful in that regard.)
-KS