If Sony's lenses are any guide, they won't be any smaller or lighter.
Projecting a full frame image circle onto a sensor at a wide aperture takes a lot of glass, that's just how it is. It doesn't matter all that much if you move the lens a little closer or further away from the sensor. Opens up a few more possibilities for lens design, but still...
Also... So now this news comes out the day after I finally got fed up with Canon's lack of IBIS and no stabilized 24-70 2.8 and broke down and ordered a Tamron?
Also, are they really going to make both an EF and an RF 24-70 f2.8 IS? That's a really tough choice to make at this stage in the game, with the options for EF cameras much more rounded out than RF.
I mean I assume the RF lens will be the one that is more relevant further into the future, as I think RF cameras will eventually take over. But right now it seems kind of limiting to by an RF only lens if a similar one comes out in EF and can be used on either EF or RF cameras.