I think that the Midjay plus is a substantial improvement compared with the old Midjay; I too am planning to upgrade as soon as it hits the market. My opinion is that, until the Audya comes out, the Midjay plus is the best unit Ketron has to offer.
Speaking of the harmonizer, the Midjay has a mic input with gain, volume and tone control but, according to Ketron, it can be used just for talking. Ketron has, however, a three voices vocalizer, that comes as an optional. My opinion is that, if the harmonizer is really important to you, you check elsewhere (the Roland G-70 and the Korg PA-2-X pro have excellent harmonizers).
Korg Kronos 61 and PA3X-Pro76, Roland G-70, BK7-m and Integra 7, Casio PX-5S, Fender Stratocaster with Fralin pickups, Fender Stratocaster with Kinman pickups, vintage Gibson SG standard.