There's nothing so far about a 24-105 II, but there is a rumor about an update to the 28-135 IS, possibly with a slightly modified FL range. That'd be great news in my book, as I think that FF users really need a cheaper option than the 24-105L that isn't a 13-year-old design. Give me an updated 28-135 with variable aperture and significantly better IQ than the current model, and I'd be all over it (well probably not, I like my current zoom).
As for the 24-105...in my opinion, which is probably in the minority, it's not good enough to merit the price. Big distortion and vignetting at the wider FLs (correctible to a degree, sure, but that correction is not lossless), often (not always) messy bokeh, and not-particularly-impressive edge sharpness. It's certainly a good lens, but way overpriced. Honestly, after using both, if I had to choose between dropping ~$200 on a used 28-135 and ~$800 on a used 24-105, I'd take the 28-135 and put the other $600 into one or two primes at FLs where I'll need critical IQ.
Also, since you don't seem averse to a second camera for group shots...you should strongly consider one of the NEX cameras (NEX-3 is $350-$450 used) or even a Sigma DP1s (around $350 used but NOT stabilized). Any of those would be far, far cheaper than a 24-105 and, in fact, take up less room in your bag!
By the way, I did almost the exact same thing that you did...I went from a 40D+Tamron 17-50 combo to a 5D2. Mine was the non-VC though. Once I got the new camera I was obsessed with finding an equivalent for the 17-50 in terms of IQ...tried a Sigma 24-60/2.8, Sigma 24-70/2.8, 28-135 IS, 24-105L, and briefly a Tamron 28-75/2.8 (I would like to one day try that one again as it didn't get a fair shake). None of them could match the overall sharpness of the 17-50 (though several had significantly better bokeh and AF speed/noise). So I basically came to terms with the fact that a big ol' standard zoom was not going to be the way to go on the 5d2, and finally wound up with my Zeiss. I'm finally happy with the IQ...but sacrifices had to be made!