You guys should really read the actual thread that was posted on the PR forums
http://www.realitymod.com/forum/f10-pr-bf2-general-discussion/82680-dynamic-sky.htmlit has alota useful information...
A quote from Mosquill himself:
"Ok, first of all, this is WIP, so keep that in mind. Secondly, it IS bf2. Thirdly, dynamic sky's main purpose is to serve as a base for the weather system I'll be working on, day/night cycle is just a bonus ability.
I've already thought about the lightmaps issue months ago, and I have a few workarounds in mind. One of them is to only have ambient occlusion on the lightmaps without shadows from the sun, the sun shadows will be rendered via dynamic shadows. The dynamic shadows draw distance can be increased to 400m (50m currently), and its resolution can also be increased. With this method you'll have both lightmaps and working sun shadows on statics.
Also, like some people have already mentioned, lightmaps won't be a problem if the sky only changes for just a few hours. Which btw, is what i intended it to be like anyway."
He also went on to say that the impact on preformance was about 0....
IMO it would be a wonderful feature... something the devs could def look into for certain maps (dawn/dusk types) when they have the time... I'm sure it's not #1 on their priority list right now, but it could be a great feature.