Napalm, P47 strike against massed vehicles,troops,towns. Would cause extensive damage to towns. Vehicles that don't move immediately start taking damage,open turret gv's(osti,M16,M3) destroys turret or pintel guns. Kills alltroops within certain area. Starts fires on bases and towns causing damage over time.
British tanks. Early war Matilda,Mid-Late war Cromwell and Churchill tanks.
Tank destroyers. German hetzer,American M10,M36 and maybe assault guns, Stug, jagdpanther,jagdtiger.
Self prop. arty. Easily done just change some code model a few Gvs. Damage relevent to size of gun, 155,105,88 etc.
New tanks. Panther, M18, Pershing, Early war M3,PnzIII.
How about a new arena if the war didn't end in 1945. Introduce the relevent jets on each side. Model some of the German, GO292 etc. New tanks, King tiger, T34/85-II,etc.
These are just some things I think would be interesting.