That was the concept of the 3rd party Sanguino board ( http://sanguino.cc/
) which is breadboard and any .1" spaced proto type board construction compatible using a more powerful avr 644P chip then available on then arduino boards (pre-mega offerings). Unfortunately it doesn't appear to be supported as to IDE versions as there site shows support only for IDE version 18 and indeed may not even be available today.
So the concept of designing and selling a DIP friendly module version of the avr mega1280/2650 is not a difficult product to produce. It just requires someone or firm to make the needed investment in hope that there is a large enough market to make it worth while. The popularity on the arduino Nano form factor does support that a more powerful version would also have a decent niche market.
In the mean time the DIP version of the mega1284 offers the most powerful, easy to implement arduino compatible chip, abet needing IDE modifications/additions.