The underwhelming optical quality of the 24-105 lens and the missing IS of the 24-70 lenses were two important reasons that have been keeping me away from full frame. I really hope that this is going to change now!
I find comments like this interesting, and a little confusing. IMO, the best general purpose zoom lens for APS-C is the EF-S 17-55mm f/2.8 IS. The full frame equivalent of that lens would be a hypothetical 27-88mm f/4.5 lens (f-number in terms of DoF for equivalent framing), meaning the 24-105mm on FF is wider, longer, and faster than the 'best' APS-C standard zoom, and still has IS. FWIW, the 24-105mm on FF will deliver better all-around IQ than the 17-55mm on APS-C. So really, nothing should be holding you back from the standpoint of IQ with a standard zoom.
Now, if you want to talk the cost of the FF system, including replacing EF-S lenses and perhaps buying even longer lenses if you need the reach on FF, that's a different argument.