A Bf109G-6/AS or Bf109G-14/AS are really the only good options to fix that gap.
This, finally something I can agree on - I've said it in the past, I'd like to see AS version 109s - their were more then a few squadrons that flew.
I flew the G-10 early in aces high, however its to late in the war and the K-4 was already coming into production - so no thanks.
Gap fillers would be better off, I believe if were going to add anymore 109s/spitfires - we need to be very wise in what we add, G-10 being so late war, would really NOT be a gap filler, more of another version that's so extremely limited to use. G-6 A/S for example would serve in a larger span of time, vs G-10 which would be limited to very Late war.
As a Joke I posed this a long time ago - if we DO add anymore 109s/spitfires, lets add one of each in a patch - kind of a tribute to both planes rather then have one group of "fanboys" whine about the latter not being added.