Now with r4370, the syntax proposed in comment:4 is implemented.
With this and the ability to quickly go to the actual changes from the displayed version using the Last Change link, I don't think it's still worth to have an explicit TracLinks syntax for accessing the differences directly… this seems a bit overkill.
Now, what can eventually be adapted is what should we preferably show when clicking on a "WikiStart@2" link: that given version (as it is currently done in r4370) or the diffs from that version to the previous one? In either case, the other view is one click away…
So let me know if you prefer the alternative or if things are now OK like that.
(Sorry stevegt about the choice of "@" over ".": I favored consistency. Besides, this keeps open the possibility that one day we'll support digits and dots in WikiPageNames, i.e. #425)