When will we see another 5 Star General?

To answer that question, you have to look at history and understand why the rank was created in the first place.

During WWI and WWII, our top commanders were being out ranked by the European top commanders. We needed something that put our officers on equal footing with the Field Marshals of France and England. Hence, the creation of the rank General of the Army, denoted by 5 stars. The rank stayed through the Korean War, where it was held by Gen MacArthur. Once he retired, it was never used again, and probably won't be until we are forced to combine with an ally to fight another global conflict.

Man, Really? We already got more Generals NOW than we had at the height of World War Two...Almost to the point that One Stars at the Pentagon make Sammiches...

https://en.wikipedia.org/wiki/General_of_the_Armies

You might all find this interesting reading, if nothing else...I'd read that Gen MacArthur had been considered for it, quite seriously, though he basically turned it down, or dissuaded those trying to get it for him...then, too, I'd read Gen Schwarzkopf had been very seriously considered for a fifth star, as well, though he also apparently declined it, I'd read, as he'd have had to been on active duty forever, essentially, I'd also read...just a cpl of thoughts...then, too, there was the whole thing with Adm Dewey, as Adm of the Navy, though I never quite knew where that fit into the whole thing, ya know? Personally, if anyone should be allowed it even in retirement, to me, it'd be Gen Colin Powell, of course, though that's just my thought on the whole thing, obv, OK?