Good for Canon to upgrade the lens, but as for everyone else, I wonder about the price.
Nikon is charging a ridiculous amount of money for their 80-400G (though prices are going down quickly). However, they could do it because the new lens is much better than the old 80-400.
Canon 100-400 is quite good. Can they do a so-much-better lens optically? I don't know, and if they do the price will be exorbitant. Certainly it will feature better IS, and I think they're going to smoothen the bokeh too - the biggest problem of the current version. So while I'm sure it will be a better lens overall, the margin could be slight to justify the difference in price. I think the MK1 will look like a much more attractive package to the most.
Talking about alternatives... never heard of Sigma 50-500? I'm holding on for my purchase of an expensive telezoom until Sigma and Tamron announce something in this range. In the meanwhile I enjoy the cheapolicius Tamron 70-300.
It's interesting. Before the 6D came out, many people claimed they'd get a 5DII over the 6D, but it seems like the 6D has done just fine and people are happy with its advantages over the 5DII. When the 24 IS, 28 IS and 35 IS came out, people complained about price gouging and said they'd never get those lenses, but some of those prices have fallen into the 400 range already. When the 24-70 II came out, people complained that it lacked IS and was priced through the roof, but people are still buying it even though the Tamron 24-70 has VC and is significantly less costly.
The problem with the 100-400 is that it does some things well, and that other lenses have eroded many of the advantages it had when it was released. The 70-200L II + 2x is said to come close in IQ at 400mm and is longer when stored and is slightly heavier with the 2x. The 70-300L is more compact and lighter and has very good IQ. I'd expect the new 100-400 to soundly beat the current 70-200L II, 70-300L and 400L f/5.6 IQ-wise, especially at the long end. It might come out closer to 3k initialy but give it a year or two. Early adopters pay a premium.
The 24-70 MK2 is optically better than the Tamron. If you can afford it and you don't mind IS, the Tamron is not a strong competitor.
As far as the rest is concerned, it's Canon offer at a certain price point. If you want a 35mm prime and you can't afford anything better than that (e.g. 35L) and/or you don't want to buy products from other brands (e.g. Sigma), there's not much of a choice. Afterwards you can only try to get the best out of what you bought.
None of those product is "bad". There's just a discrepancy between their price point vs performance ratio when you compare them to other offerings on the market.