i believe that the thing holding up the rs6 is simple:
1) quattro is still making the rs4 with strong demand for the car still;
2) the s6 has just been released. audi wants that to have a reasonable run as the c6 "halo" car before the new "halo" car is released.
these are also the reasons why the rs6 will debut before the rs5.
as for price - i hope that make it more expensive and reduce the quantity made. my rhd rs2 was 1 of 3,000 of which only 1/10th were rhd. the result was excellent residuals. i believe there have been 6,000 rs4's to-date with production still continuing.