Don't think it'll be an L, just a good EF with a long reach. My reasoning is, this doesn't seem to be the exciting and eagerly awaited 100-400L replacement, as I would have hoped for bigger apertures over the current 100-400L, and I doubt Canon would have two L series zooms that are so similar, e.g. 70-400L and 100-400L2.
If this is the 100-400 replacement, then it will need to have kick-@r5e IQ if there isn't an improvement in aperture, and please deliver it soon!
Just my two penneth.