Yeah that's a valid way, I don't deny it. But the "asynchronousity" of the pathfinder makes it a bit of a pain to implement.
(I think even the map generation is asynchronous and there's no trigger for that... might have to request that)
And as far as speed goes, he only does that on start of layout it seems. So.. it should be ok as long as he doesn't have more than maybe 2000 grid cell (since I used recursivity, you might stack overflow)