I have to complain about the game lacking the Panavia Tornado. Cool aircraft, and was very fun to fly in AC6 (can't recall if it was in ACAH), surprisingly capable in air combat despite being nominally an attacker.
Wonder what aircraft the DLC/Season Pass will include. If they'll go with purely original aircraft (to avoid licensing costs or whatever), it seems likely that previous "superplanes", the ADF-01 FALKEN (multiple games), CFA-44 Nosferatu (AC6, ACAH DLC) and ASF-X Shinden II (ACAH DLC), or variants of these, could be plausible.
There aren't many modern planes (at least commonly know) missing from the game as it is. Variants of existing planes would be quite lackluster. The Harrier perhaps, but its VTOL feature would be likely hard to depict reasonably without additional controls, and this is likely the reason why the plane's in the game but not playable.
Perhaps they'll go for older planes, after all this game features the the F-104 Starfighter and MiG-21 (and F-4 with pre-order DLC). There's many to pick from after all, some notable ones being A-4 Skyhawk, F-5 Freedom Fighter, F-105 Thunderchief, F-111 Aardwark, F-106 Delta Dart, F-100 Super Sabre, MiG-23 "Flogger", MiG-19 "Farmer", Su-24 "Fencer", Su-25 Frogfoot...
EDIT Or some European ones: Dassault Mirage III, SAAB Draken or Viggen, Panavia Tornado.
I would get a DLC Shinden, hoping they release the sci-fi planes personally.