good idea, but for the most part this exists in sashimi.. a cab combining tool...
check this out..a few links imbedded through the post as well
http://forum.xda-developers.com/showthread.php?t=476687
according to this, you cant realy do 1 big cab, it cant process all the data.. also any cabs requiring user input have to be done seperately still or atleast grouped together i think...
you can remake,not combine, a cab that includes all ur stuff...but it would get pretty signifiant in size if u have alot of stuff