The only reason why the ACD with DP was still around was for the old MP. It's no longer necessary.
Since Apple stopped selling the old MP, it stopped. Not because of something necessarily new.
I have to assume that a new Apple display is going to come out soon.
That is far more so coupled to the iMac reaching steady state since the Thunderbolt display is basically a mutated iMac.
It will make sense why the new rMBP has TB2 and 4K support via HDMI.
HDMI 4K is for TVs, not computer monitors. It is sub 30Hz 4K which is fine for reference monitoring movies. There is about zero need for Apple to come out with a "movie reference" monitor. 3rd parties have that covered now and even more so in 2-3 months after CES 2014 and the 2014 product launches start. Apple is probably not going anything with 4K monitors this year at all. The prices are volatile ( relative to what they will be in 12-24 months ).
TBv2 on rMBP is a bit surprising, but certainly will drive deployed TBv2 deployment volumes... which is why decoupling from those doesn't make a lot of sense. We'll see if Apple turns TBv2 into a "FW800 for pros and kneecap for extended period with FW400 for the rest" approach of artifical product gaps. [ If Mac Mini comes in 2013 and with TB2 ... then it was only a matter of time of year and parts availability. ]