If they do go to Disney Paris and do the race there, they might as well bring the U.S. back into play and put a race to WDW in Florida. Florida already has its fair share of races like Daytona 500 and Sebrings 12 hour race. How great would it be if F1 came there too. The airport could handle the extra guests and Disney and the Orlando area Attractions would become a popular destination during that week before and after the race. I think it would make a prefect family vacation deal with and F1 race tagged on.
So parking, and working within the exiting crowd flow, is a problem with putting massive event like this within a theme park resort.
Granted, there's still a fair amount of space at WDW (have no clue about DLP), but Disney's decision to build the oval at the end of the MK parking lot doomed that race. An F1 track, if purpose built, would need to be located a fair distance from the parks (at either WDW or DLP) in order to ensure maximum flexibility on scheduling.
In Disneyland though, as far as my knowledge of the resort grounds goes, they have enough room to build a couple of more parks, so they do have enough to build a track for an F1 race and other races what it most likely then would be used for. Just what their traffic is like....no idea