Would be interested in your opinions too.
A driver of this size usually already starts to beam at the crossover frequencies, which are possible with the Mundorf 25D1.1. I think, 2000Hz is the absolute minimum, which the Mundorf can handle. (I tried it out with a crossover implemented with Acourate).
However, the radiation pattern of a dipole is determined by driver size and baffle size (and shape of course).
It could work, but I'm not sure, if the directivity at the crossover frequency of this combination would be excellent, good, acceptable or poor (depending on your standards).
With the 12MU however you would be on the safe side, but this would mean an additional way and hence more complexity.