A lot of what we do in the vertical slice model would be a lot easier if we could combine together our u-w components of our velocity field (stored as an RT field in the slice) with our v component (stored as a DG field in the slice) so that the basis functions are 3D vectors on a 2D x-z plane. In particular, then I could assemble the inverse of the combined u-w-v velocity mass matrix combined with Coriolis, and make things a lot more implicit in the Coriolis term, leading to bigger timesteps when we sent the Coriolis parameter to infinity (something we have to do in our test case unfortunately).