Not only dreaming but silly
i don't think 128, 256 or even 512bit bus on a card like this would have a noticeable effect on it's performance as with GDDR5 these days the bandwidth on most cards is more than high enough thus why GPU core overclocking normally gives the highest boost.
I think GDDR5 is the perfect solution to low end chips as a small bus can give a useful amount of bandwidth meaning it is easier to keep these chips as small as possible yet have a bit of kick to them.
I have a 64bit bus with GDDR2 on my 40 stream processor 3450... useless, a 64bit bus with GDDR5 and 160 stream processors on the 6450? now that's starting to become a more useful amount of power for min settings gaming.
On paper it happily beats out some of the mid rage cards i have used from only a few generations back.
Think about it, a generation or two from now the low end cards could easily carry a 64 bit bus still but it could be paired with GDDR5 running anywhere up to say 6ghz, I'm pretty sure that would pump out a fair bit of bandwidth even on a 64bit bus (i would do the math but it's 7am so no
).