I suppose a lot depends on what exactly is their purpose with this 'generations' thing. There has been a lot of speculation about the idea that each of the 'generations' will be showcased in different books. If that's the case when we could very well have a situation where, for example, we have a 'Superboy' book with Clark Kent in Smallville (potentially teaming up with the JSA and Wonder Woman), a 'Superman' book with a young, single Superman during his heyday, a 'Superman' book with an older, married Superman, and a 'Superman' book with a grown-up Jon Kent taking over the mantle.
I suppose that's one way to solve the endless arguments about who's the 'best' version of the character!
In a sense, I suppose it could work. People want to see these characters as evergreen, unchanging 'brands', but they also appreciate character development, progression and in some cases succession. Comic book time is ultimately a tug of war between these two approaches, and DC is perhaps finally ready to let the rope break and just let both sides have a win.
Let's not forget that some of the most iconic interpretations of characters are either from other media, from comic-book stories decades in the past, or from 'out-of-continuity' Elseworlds/Black Label style stories. Maybe its time to break away from the rigid idea of a 'mainstream' present-day continuity that will only have the illusion of change and allow it to change...while showcasing more classic interpretations (or reinterpretations) of the character side-by-side.