I wouldn't mind seeing light recon units either, if only to simulate meeting engagements between recon forces.
As for including different shell types, I think the rules handle them pretty well as is. Tank's antipersonnel attack incorperates the machineguns and HE (especially with concussive firepower), whereas the anti-tank attack deals with AP rounds. Personally I think it would be acceptable to use the antipersonnel attack as a "light vehicle" attack as well, so that HE only units (like assault guns) could still take out halftracks and trucks and the like. Thus you'd be treating the two attacks as a "soft target" and "hard target" attacks instead of vs. personnel and vs. vehicle. This would allow you to add howitzers that are effective against infantry and lightly armoured vehicles, but only effective against lighter tanks, which is pretty realistc. I'd only add that for the vehicles though, not the infantry.
As far as some of the other things that were mentioned, I think that goes beyond the level of detail for Tide of Iron. Do you seriously want to get into modelling the difference between a .30, .50, and MG42? Go play Flames of War or ASL in that case. The reason I like Tide of Iron is because I can actually convince other people who aren't wargamers to play it with me. Don't get me wrong, I love complex games (SFB remains one of my favorites) but I think that level of detail goes beyond the target audience for ToI. But hey, there's nothign wrong with adding some house rules for things like that (I've already designed a very simple system for tank arcs that works amazingly well).
For new units, more than anything I want to see an Operation Barbarossa expansion. Units, in particular I'd like to see: T34/76, T34/85, KV-1, as well as some early war German units like the Panzer II and Panzer 38(t).
Units I'd like to see in general for all nations include primarily howitzers and recon units. I also wouldn't mind seeing rules a couple of Sherman varients like the 105mm howitzer version and the British Firefly, and maybe a Cromwell (which in game terms would probably be the same as the Sherman, just included for variety). Though one unit I'd love to see is a Churchill tank. Armour nearly as strong as the Tiger, but slower with a weaker gun. This one could be included in the Soviet expansion as a lend-lease unit.
Anyways, that's my $0.02.
Also , who died and made you the boss of Me???