Is there any way to have a text-based Extended BG Color Mode in 80 columns, like on the C64? Ideally, I'd like to have each 8x8 cell have its own foreground and background colors. The goal here is an 80x50 fast graphics mode. Thanks for any help...

Unfortunately the answer is NO, it can't be done in text mode.  It would have been nice if the designers would have put a bit in one of the registers to turn off the attributes and use the upper half of the color data to store a seperate background color.

You have to use bitmap mode if you want to color background and foreground in each cell.  Unlike the VIC with fixed 8x8 cells, you can have a different cell size with VDC.  In fact you have to use a larger cell size (or a smaller bitmap) on a C128 with only 16K VRAM.