Whenever it comes to dynamic elements you have to make sure to clearly state your term of "dynamic".
As i would understand it, it means to be able to fully control its features at any given time.
As for a sky system you also have to make sure to tell what your idea here is.
Is the sun casting a realtime shadow, will it change color and atmospheric haze over time ? Are there clouds and if so what is their influence (sunlit, scatter, change of shape casting shadows etc.. )
Sky is a complex element and one should think about how much features are needed and in what way.
also the todays skyboxes are actually domes due to the fact that there is a much better perpendicular surface which prevents distortion and todays cards can handle more polygons than a few years ago.
First and most important is the overall texture of the sky. This could be a color gradient (small memory print) or some photo or 3d render based average image including haze, clouds and so on.
If you use clouds in your sky texture, be aware those are static, so you could only move the entire texture\dome. Alternatively you could move clouds on their own layer in front of the pure sky.
Sun is a critical element here. If you really need it to move you would expect dynamic shadows and lit surfaces. This is something cafu is unfortunatly not really good at. You could have the sun cast shadows but the performance would pretty much drop due to it's hard shadow nature, and it would not look very natural as there is no penumbra (spreading or softening shadow based on distance)
Thats why Doom 3 only had few small outdoor areas.
But you could do a setup where you would blend between different stages of times .. if on cycle would really take a 24h of actual time that would be no problem.
For example Bethesda's "Fallout" Engine does NOT cast any shadows for environment elements like trees, stones and all that is outside , yet it does look really great !
It would require that terrain is not lit by a primary source but rather diffuse lit, like an ambient occlusion based approach, then lit surfaces with one primary light that does not cast shadows.