I think it's a great idea, we had a 4x8' HO table when I was a kid and tried something similar. A couple of thoughts:
-As someone has already pointed out, it makes sense to "overengineer" the supports and eye bolts, as this is likely to get heavy.
-Test the rigging - you are going to want a pully system that lowers the table uniformly. That might sound obvious, but if you don't deign it that way you will be tempted to think you can lower it level by hand . . .not always as easy as it sounds.
-Putting it up sounds great, but you also need to consider what you are going to store below it. Cars, etc can be easily moved. If you find yourself using the space for storage, powertools, etc, then when the kids want to play you either A) have to move a ton of stuff or B) tell them you don't have time . . .which defeats the whole point.
Please post pictures of the project!