IS is not necessary for focal lengths shorter than 100mm if you know how to hold a camera well IMO.
Having IS on those short primes is just plain ol' stupid, and will only drive up the cost of purchasing the lenses. I really hope they don't include IS on the 24-70 because that will drive up the cost as well.
Must admit having IS on those very short lenses is a bit of a baffler - even handholding you won't notice much shifting of the frame unless you have a very bad case of handshake. I can only assume that the optical cost of adding them (ie optical performance) was marginal to nothing and so they put it in to have as a feature over competitors; having companies like sony pushing in who like in-body IS might well push Canon (maybe Nikon) into adding more IS to lenses, even if its not needed so that they can also boast a high amount of IS in their lens range.
Not having it in the zoom makes sense though, the current zoom is a workhorse for many and if they've boosted optical performance anything like what they did with the 70-200mm MII then that new zoom will be a near prime sharp lens through its range. Droppings its weight will also attract some since "the brick" is a nickname the current one has earned .
Ahh true video would certainly benefit from the addition of IS, I'd forgotten about that.
As for second hand I'd fully expect the second hand price of the 24-70mm to rise. The original will not be put out of production and stock quickly dwindles down to nothing. With the new version hitting shops at a higher price the second hand original (which is still pro series glass) will quickly rise. This happened with the 70-200mm f2.8 IS L when the MII came out - not long after the second hand price was near equal to the original new price of a few years back.
So I doubt you'd be able to get hold of them cheaply - you might get a lucky window - but anyone selling the old to upgrade is going to want a good price on it - so that they have to invest less to upgrade.
Thing is people that need IS get the 24-105mm which is also parfocal (retains its focus point as the zoom adjusts) and so the ideal choice for the video fans. I suspect having IS and making the 24-70mm parfocal to compete would not only run it into competition with the other lens, but also have resulted in a heavier, more complex and more expensive lens.
You say that - 70-200mm f2.8 IS L price second hand jumped up high when the shops ran out of stock when the new one came out. Lenses, esp professional series ones are not like camera bodies - and especially so since Canon is using its new wave of releases to also jump the price.