I won't ditch my 360 elite for a new model. The games will still run on normal dvd's so there is little point i think.
Adding another model for the 360 would increase the number of SKU's to 4 which is abit much and could be confusing for consumers.
An external blue ray drive is probably the most plausible but considering the hd drive addon didn't sell much, i doubt they will add another with no prospects for huge margins of profit.
I think Microsoft is best off pushing for downloadable movie content.
I think this deal you wrote about is for Microsofts next console which would make sense as blue-ray should be used on the xbox 720 without a doubt.