Is Metarouter supported on mAP 2n? The wiki page lists a number of MIPS boards (RB400, RB700, RB900), but not mAP 2n.

no, it is not possible to run MetaROUTER on mAP 2n.

Any plans of adding Metarouter support for mAP 2n?

Why can't the image for e.g. RB951-2n be used, as they are based on the same chipset (AR9331)?

there are differences in hardware that do not allow us to run metarouter on mAP 2n.