It would be silly to assume that any of the three manufacturers would not already have quite detailed plans for the next generation, and most definately have conceptual plans for the generation after that.
Especially Sony needs to concider how the next playstations fit in their other home entertainment concepts during the next 10+ years. MS would also have some idea of how the future versions of Windows and especially DirectX could benefit from the development of the box and vice versa.
I think Nintendo is (again) the most interesting player, since this is their main branch of business, and they have no actual need to, for example, implement any media center capabilities if they don't want to and they don't need to concider compatibility with other systems apart from the legacy platforms. It is very likely that the nintendo consoles will always be the less powerfull, have less features outside of the immediate gaming scope, and be the cheapest of their generation.
Also, I think that Microsoft will again offer the most conservative option of the three, given their relationship to the PC world and the requirement for the console development to also benefit the Windows development. They are the most likely to rely on tested technological solutions and existing hardware types for the same reason.
All tree are most likely concidering storage and distribution issues for the next two generations to come. Will the content be streamed or downloaded to be run locally, or bought on discs from local shops. What kind of local storage technology will be used, if any. What kind of controls are used apart from the legacy controllers, and are control devices attached to the user or separate (some have speculated the use of multipel cameras to replace hand held controllers). Etc.