I guess I have to say they're kind of sexy after further thought. Not because she's Uber skinny, but because you can almost sort of see her naughty bits even though she's clothed (not much, but it counts). Sort of like a down the blouse glimpse of tatas. The little boy in me votes yes for unintentional naughty bit observatories. The man in me says she's so skinny I'd be afraid of breaking her. :-)
I just heard about this today too. I think it's better than the thigh gap. Loads of girls have a bikini bridge when they lie down. Some even standing. It's far more attainable than the thigh gap where it pretty much depends on your build rather than fat levels. On the flip side fat is more likely to be displaced when lying down than muscle so it's a bit misleading. Either way I don't like these measures that teenage girls follow for "perfection", at least this one gives them better odds even if they are carrying a little weight.
For me I don't like my bikini bridge. I always put my ipod on my bridge so nobody can see down my pants.
Same thing with thigh gaps. I don't care for them really, I just feel neutral about it. If you happen to have either I don't think it makes you even more or less attractive. You can't really help if you have it to begin with and I don't think there's much you can do other than gain weight to try to conceal it, but that's besides the fact.
I seen a story elsewhere about this calling it the "thigh gap" of 2014. I didn't read much of it as like with the thigh gap, I thought "Really?!" Makes me wonder who starts turning this stuff into a trend or fashion statement.
I have a variation of what I find attractive in a lady. I think a girl who fits into a hug nice, but I also find the idea of a fit woman nice. I'd think that neither woman would have a bridge (sounds weird saying that). So I'm going with the notion that girls who have these probably are going to be too thin.
On a related note I've rarely seen girls in bikini's so I doubt I'd be like "Hey, lay down and lemme see your bridge clearance!" :P
I think it's really sexy to have a little gap either side, but not to be so thin that the bikini doesn't even touch your stomach - although I'm sure it's possible for some women to have bikini bridges without being underweight at all, depending on their bone structure.