My take? Build a NOS-styled resort hotel on the area North of DTD (behind the former ESPN/Rainforest Cafe). Do a exit-only bridge into DL for after-hours events (or exit valve for Fantsmic). New guest corridor from the parking garages goes through the middle of this resort, made to look like the French Quarter with new shops/restaurants on the ground level as an expansion of DTD.
Area South towards Katella becomes DCA's second entrance/exit, and new lands. Two new bridges make a loop near Sky School/Pixar Pier over the road, and adds two new lands (minimum) and multiple new rides. Toy Story Lot becomes a waterpark with attached hotel, either indoor like Great Wolf or outdoor like Volcano Bay/Cabana Bay.
That gets you new premium hotel options and an expanded DTD, some fixes to DL traffic, another gate (even if it's small or resort/only), and more importantly new lands/rides at DCA. Not sure DL needs to grow while there are still some big projects like Tomorrowland sitting around, and I think there are some diminishing returns for expanding DL's footprint, which already is more than a one-day park experience.
If they really want to get wild with it, throwing more upcharge/timed-ticketed experiences at the resort is always a way to do it.