That's a great idea! Because it is great for guests and would permit park hopping, however, you can be sure that WDW would never allow it. I think they want to eliminate park hopping altogether -- again, following the recent trend of crapping all over the guest experience for the sake of raking in more cash. Two (or for some people, three) of WDW's parks can be toured in less than a day before hopping to another park, and I think Disney has figured out that they can get guests to stay in a resort and eat on-site for more days/nights if they're
not allowed to park hop, since only one park a day for most people means more days needed to tour all four parks (or six, if you visit the water parks). I suspect that that WDW makes more money per [average] guest off of an extended stay in an onsite hotel (plus extended-length tickets) than they would for the same guest through the parkhopper add-on. Not to mention the fact that after a guest has toured a less-than-full-day park, they're more likely to head to Disney Springs and shop, or schedule a fancy dinner at a resort table service venue, or rent something at their resort, or book an expensive hard ticket event, or otherwise drop more cash into WDW's wallet out of sheer boredom, if they can't hop elsewhere.
For example, Epcot is a 1 1/2-day park for my family. It used to dovetail nicely with a 1/2 day at the Animal Kingdom. If we wanted to stay onsite and pursue the same plans and couldn't hop, we'd be have to spend 3 days/2 nights on property instead of the 2/1 we'd spend with parkhoppers. (Same thing with MK/HS). We're going to outwit them, however! Instead we'll just spend 2 days at Epcot, skip AK altogether, and do a lot of loud griping about it.