I've been asked several times now: is it best to get a DP Merrill camera or wait for Sigma to release the DP Quattro series? The answer to that question is not easy.
First, while we know what the Qauttro cameras will look like, until they are released it is difficult to know how they will perform. They are supposed to be an improvement over the Merrill series, but some theorize that, yes, there are improvements, but at the cost of some aspects of the Merrills that people like. So until photographers get their hands on the Qauttro cameras, it is impossible to say what you are actually getting with it.
Second, one must consider the cost. No one knows what Sigma will charge for the Quattro, but rumors are $1,000. It could be more, it is unlikely less. Merrill cameras can be had for less than $700 right now. The price will likely drop further once the Quattro series becomes available.
Finally, Sigma has not announced when the Quattro will be available. While it is should be soon, it may not be until around Christmas.
So should you buy a DP Merrill or wait for the DP Quattro? I can't answer that. Perhaps wait for the Quattro series to be released, then buy a reduced-price Merrill. Or take the plunge now and get the Merrill. Or wait to see if the Quattro is significantly better than the Merrill cameras. Whatever one of those situations most appeals to you is the path that you should take.