One with the Force is an ability upgrade that turns in to a support. Neither of those are taken by General Grievous, he takes non-ability upgrades. I agree that his ability very much sounds like a Redeploy to Opponent, that triggers before your own redeploy, so we play it that way, with the die going to the card. Someone should ask FFG about that though.
Nobody was suggesting that he takes One With The Force.... at all.
RRG states that each player has their own play area
DICE POOL
This is where dice are rolled. Each player has their own dice pool. Dice are always placed on their matching cards when not in a dice pool.
OUT-OF-PLAY
Cards in a player’s hand, deck, and discard pile are out of play and their abilities cannot be used until they are played.
- A card leaves play when it transitions from the play area to an out-of-play area.
DICE ON CARDS
When dice are not in a dice pool, they are placed on their matching card.
- These dice are not active, cannot be manipulated, and none of their sides are considered to be showing.
What you pasted from the rules only states that each player has their own dice pool, not that each player has their own play area. It does reference a Play Area, but not that there are two of them, each belonging to a player.
I think, at least for now, that Grievous' ability was intended to work like redeploy. Until we get further clarification - I would probably play it that way and if there was a tournament tomorrow would probably rule it that way as well.