A very good question. Right now, we're planning on merging diffs as best we can into the tree. However, we think the ACS can be vastly improved. We're not talking number of features or number of modules (although that, too, can be improved). We're talking about the core structure, the modularity, the ability to easily extend it without stepping on other people's toes.
Starting in April, which is when we hope to come out of beta, unless the ACS/Oracle becomes much more modular, we're going to branch. We'll still try to keep up with features, but we have no reason to keep up with the actual code.
Please comment on this, though, we want to hear what the community thinks.