JAL has postponed the purchase of Regional jets until at least the first quarter of 2007.

Source Flightglobal

No surprise.
RJs are a rarity in Japan will continue to be so because of the economic setup in Japan & slot situation at the big two domestic airports.
80-100 seat RJs can be viable on many of the runs from Tokyo/Osaka to some of the smaller regional communities that only see one or two A320/737-type flights a day, but only if the number of slots at HND/ITM doubles. Otherwise, any Japanese carrier would only need a handful (less than 5) for connecting any two small cities in Japan. Is another type of aircraft useful in such small numbers; most likely not.

Weren't these suppose to replace or expand service for J-Air out of Komaki (NKM)?

That is RJ heaven now. J-Air is supposedly going to increase the number of flights out of NKM to meet a demand by those needing a quick business connection and don't want to go all the way to NGO.

I don't know if I'd call NKM a RJ heaven even though anything scheduled is a J-Air CRJ. What is there something like 20 flights a day there. You could easily get that in 20/30 minutes at CVG or MEM.

Unfortunately, anything over 56-seats on a scheduled flight is not allowed into NKM.