I think that the real damage to both Microsoft and Sony would be felt in the next generation if these add-ons are not particularly successful or well received.
First off there is the third party factor, and while these Playstation Move and Project Natal games are unlikely to be as expensive as most PS3 or XBox 360 games it is likely that they’re significantly more expensive than their Wii counterparts; and large losses from products supporting failed add-ons after betting against the Nintendo DS and Wii will likely be the last mistakes many executives at third party publishers make for these companies.
Secondly, I would say there is a risk from core gamers feeling abandoned especially if Sony and Microsoft continue efforts to be more inclusive in their next generation. After last E3 core fans of Sony and Microsoft spent a lot of time hyping that their console’s new input devices would be used heavily in core games and their systems would have the hardcore gaming experience that Wii owners had been asking for since it launched. If these add-ons launch and the smaller core titles (that I said should have been made for the Wii) are replaced with the kind of motion-controlled shovelware that the Wii has been bashed for it will aggravate a lot of these gamers; and if these systems are unsuccessful and Sony and Microsoft continue to push heavily in this direction the feeling of abandonment will only get worse.
Finally, there is what I would call the Zune factor. If the expanded audience doesn’t see value in these products it will become dramatically harder to catch their notice in the next generation (regardless of what you do).
