IMHO gidlines & ticks will be the hardest part of this proposal. As it stands, the standard matplotlib ```Axis``` is quite restrictive and requires a specific ```Axes``` interface to provide very specific ```Transform``` instances. The ```AxisArtist``` does make some of this easier, but it is non-standard and has some significant limitations which are hard to address without a complete re-design. I've done some work to allow gridlines (and limited ticks) in cartopy - it's certainly not polished, but I'm sure we have some overlap here and I'd be happy to help out. Ultimately, I'd be in favour of overhauling the whole mpl Axis implementation (there can be significant simplification, and I believe optimisation, which mpl would benefit from) - but that certainly widens the scope of this proposal which may not be wholly desirable...