*** Late post to this subject!!
I think we're all thinking about this from a British perspective.
In Bangkok, Thailand, these u-turns are quite standard at Roundabouts. In Thailand most roads are dual carriageways and there are many minor roads which join on. Thailand usually uses a one way 'local road' system either side of dual carriage way and there are also various filter lanes that shuffles traffic around.
Things to keep in mind why Thailand uses the u-turn system:
1. Far higher volume of traffic than anywhere in the UK.
2. More cycles and motorcycles (so they don't have to navigate the roundabout)
3. De-regulated traffic (ie it's chaos)
4. Less traffic on the roundabout.
and snoop about.
I had a quick look about, and all the examples of U-turns I saw were joining slip roads under GSJs. Compared to a u-turn between the two carriageways of an at-grade DC, this usually has the advantage of space - the two 'carriageways' (slips) typically have an entire D2+ between them. That reduces the tightness of the turn and increases stacking capacity.
There is in fact a related British example
on the M8 (soon to be M74, probably), though here the space is bigger still since there are two D3Ms between them. This example, like some of the Thai ones, involves a diamond type interchange rather than a roundabout interchange - and indeed, there is as much reason for removing traffic from a signalized cross roads as there is from a roundabout.
As I mentioned, I really like the idea of u-turns at busy junctions, where there's the space, which in the UK usually means at flared roundabouts. However, the fact that they involve a right hand entry and exit probably prevents their widespread adoption in the UK - of course, when traffic is chaotic anyway, as in Thailand, this is less of a barrier.