Any thoughts on the recent new Mitsubishi Heavy industries Ltd Regional Jets, and how it will affect the airliners duopolic market of Boeing and Airbus?

From Wiki:

The passenger size of the MRJ is 70-90.

The smallest commercial Boeing jet B737 can carry 85-215 passengers.

The smallest commercial Airbus jet A220(former Bombardier C-series) has passenger capacities of 108-160.

It appears the MRJ is not competing in the same market as Boeing and Airbus. The MRJ would probably appeal to airlines that serve/want to serve short haul flights with a lower passenger load i.e. island hopping or domestic flights. Or as a private jet option.