I think the first thing I would say is that if we think about the key requirements that one would expect Parliament to bring to these various documents and pieces, you essentially need to be able to hear what the government is proposing to do in the budget, and then you need to be able to track what it's doing through a succession of reports, estimates, documents, and other information sources.
Personally, I'm not sure that the sequence of these various reports is the critical matter in the tracking. As long as every document is quite clear about what it is and what's in it, and explains clearly how the other documents add supplementary or complementary information, it should be possible to track the story.
Having said that, it does seem odd to have what appears to be a kind of mingling of different fiscal years, where you get the budget and then you bounce back to the main estimates. Personally, I don't understand why the timing couldn't be altered in a modest way by moving the budget forward, possibly into late January or early February, as soon as Parliament comes back, and then moving the estimates tabling to later on.
As we already recognize, the deadline for placing the estimates before Parliament has no substantive consequence. The estimates are placed before Parliament and then they sit there for several months before committees get around to examining them. I don't see why you couldn't move the main estimates later into the spring, into May perhaps, and that would allow a considerable portion of the proposals in the budget to be costed specifically and put into the main estimates.
Let's remember, too, that the main estimates are called “estimates”. If they're not dead right, then there are plenty of opportunities in supplementaries later on to correct that. If that were done, you would have a sequence that starts with the budget and then merges through....
As I said, I don't know how much stands on this, but certainly that sequence is more obviously logical and transparent.