I've been attempting to put together an overview of the various theoretical motivations that have been proposed for do-support in the literature, but the topic has been frustratingly difficult to research.
What I'm looking for specifically: analyses that address the universals of syntax and morphology that give rise to do-support. Typologies of do-support, essentially, rather than analyses of do-support in particular languages. Grimshaw's Last Resorts: A Typology of Do-Support is the best example I know of.
Can anyone here point me in the right direction?