As for your question: I've run into a couple scenarios that require "lookback" into the parsed Dataset to parse correctly. For example, parsing Native PixelData correctly requires looking back for the Rows Element, Cols element, BitsAllocated element, etc in order to correctly parse the NativePixel data. The futzy thing is that these context "elements" need to come from the current Sequence (if parsing within a sequence). So, I do most of my parsing of sequences recursively, with each recursive frame holding pointers to the already parsed elements in this sequence (it's a stack essentially for nested sequences).
Not sure if that answers your question? For most generic elements though, as a parsing library I try to parse it generically and make the value payload available to the caller in case they need to apply any special logic to interpreting it. Though if you have a specific usecase that needs something that is missing here, please let me know or open an issue :).