WhiteBlue - Grooved tyres could be used to adjust grip levels, but not tyre stiffness, not significantly, anyway. I understand that Bridgestone believes that current problems arose because the relative contact patch area gain resulting from the change to slicks was greater at the front than the rear. That might well be a factor. However, teams had problems before slicks were introduced, & if contact patch area had been the sole problem, it is hard to believe that a solution could not have been found by adjusting cambers & tyre pressures.
I also understand that Bridgestone has proposed that the front tyre size (presumably width) be reduced for 2010. That would probably reduce vertical stiffness by itself, but they might also take the opportunity to further reduce stiffness with a construction change. That could be entertaining if my thesis is correct (especially given the current aero regulations), because teams would then have the opportunity to engineer themselves out of their current "corner".
The situation with KERS is interesting, because it is useless until acceleration becomes power limited (unless, of course, it is used for traction control - but that wouldn't happen, would it?). The earlier it can be used when exiting low speed corners, the more effect it will have on lap time. Hence traction is important. Traction, for an F1 vehicle, would by improved by a) moving the centre of gravity aft, b) moving the centre of pressure aft & c) controlling rear contact patch load variations more effectively. My thesis would suggest that the first two might be improved by reducing front tyre stiffness, but all three could be improved by increasing rear tyre stiffness. The fact that a GP2 rear tyre (for example) has a vertical stiffness that is higher by the equivalent of around 10 psi suggests that such a change would be feasible.