The idea that a German culture after thousands of years of alternative development automatically and solely gets panzers and ditto any of the later specials seems silly.
I believe there is a better alternative for these units.
Let me begin by saying that I've always been disappointed that military technology is automatic -- you invent the automobile and you get armored warfare; invent more modern techs and you get stealth warplanes.
The special units seem relatively evenly distributed across the game's time span. IF there are enough spare technology slots, perhaps each civ could choose to develop any and every special unit. It would require a digression from pure tech development -- e.g., you might discover advanced flight, and choose to have your next tech advance be the F-15 -- and the ONLY thing that effort gets you is the ability to build F-15s. THIS MEANS THAT MILITARISM HAS A REAL COST, potentially much more like the real-world arms races with dreadnoughts and nuclear weapons.
It also means that in an alternate universe the Iroquois might have the most natural progression from mobile warfare to armored warfare, and the first blitzkriegs would be on the Great Plains against Aztec infantrymen ... And that's the sort of possibility which makes Civ so enjoyable for me in the first place.
A whole tech for one unit would be pretty time consuming to pull off. An F15 in the game isn't so special I wouldn't think, it's more or less a slightly modified fighter - good, yes, but another civ can live without it.
Aside from that, it's workable enough. Still, with the ability to toggle the special unit option on or off, I think it'll be fine.