The only downside I can see to a swing-out design like this is loss of the ability to drive with the rear gate down. Every now and again I have to use my 4Runner liek a truck, and carry something long - the only way to fit is w/ the gate open and hanging out the back end.
Honestly I don't know any way around this problem, save making the tire carrier removable. But we all know that "removable" and "durable" don't really go together.
Although, sometimes I wonder is a hitch-mounted deal might work, kind of like the L-shaped ones you can get for bike carriers... but w/ the weight of a tire, I don't know how it wouldn't wiggle around in the hitch receiver. Something like that would be ideal for me, 'cause I'm happy w/ leaving my spare under the truck in nromal driving mode, would need it only for off-roading when the clearance and access is needed.