I've recevied some more info about a possible replacement of the 50D/5D Mark II.
The source says a new xD camera is imminent.
The DSLR lineup from Canon will be as follows.
1000D / XS
500D / T1i
550D / T2i
5D Mark II
1D Mark IV
1Ds Mark III
There could be some truth to this, if the price of the 7D is cut like the 5D Mark II's has been.