Maybe a few DM/FM revisions, which we shall not discuss here.Some engine and graphical improvements brought over from BoS, including better netcode.A small number of new planes, most importantly a few of the late-war dogfight crowd pleasers, think Sopwith Snipe and Siemens Schuckert D.IV (yes I know you'd rather fly an unarmed B.E.2 in 1915, me too, but that's not going to draw in crowds).All the planes, weapon mods, maps and campaigns.Here's what a Rise of Flight 1919 could look like to be in line with that Spirit of '46: It's certainly one of the reasons why IL-2 Sturmovik 1946 remains the most popular multiplayer prop sim today (we don't talk about War Thunder). In many ways, having a single monolithic release at a reasonable pricepoint some 7 years after the initial release of the product, is what pulled many people (back) in.
Jason, among other things, talks about the "Spirit of '46", capturing what made the full release of the original IL-2 Sturmovik so popular. If you haven't already, read the announcement over at the IL-2 forum about the upcoming theatres.