Musescore is a great typesetting engine most scores, but it has the limitation of being 100% real time, unlike LilyPond, which can take the time to typeset the "perfect" score.
Being real time limits the computations Musescore can do before becoming really slow. On my machine it is already pretty slow when editing scores in Page View mode (it is very fast in Continuous View mode, though).
I'd like to suggest 3 features that would benefit from non-realtime typesetting:
1) Breaking the score into lines, trying to keep the spacing inside each line as even as possible. Musescore's line breaking is not even at all, especially if you insert a page break for some reason.
2) Adding space between staves that have dynamics or other elements between them. This should be feasible in real time, but in batch-mode we could use more sophisticated approaches like a skyline algorithm or something similar.
3) Placing notes in multiple (> 3) voices on the same staff. This is quite easy to do manually, but it would save some time if it could be done automatically. Again, this could be done in real time, but doing it in batch mode is probably easier.
The idea is that there would be a button / menu item you could choose from the GUI for each of these actions.
The program would then freeze and typeset the whole score (LilyPond-style) and unblock user interface again once the changes had been made.
I think Musescore is an amazing program, and I would never want to use LilyPond to edit a real score again, but I think we could use the best parts of LilyPond's batch approach for those adjustments that would take a long time to compute and are boring to apply manually.