First of all, i think this is just a nice brainstorming session since there's much to be fixed in the sim.
However, that doesn't mean we can't get some ideas rolling, it's good, creative and might give both us and the developers some pointers on stuff that will enhance gameplay and sales, so that they can include it in a future update/expansion or we can get to grips with it once the SDK is released (if we can "build" new flyable aircraft).
With that out of the way, here are my suggestions for the future.
I'm not entirely sure if they were in service during the BoB, but i'm a big fan of the Catalina.
It would be masochistic to fly in multiplayer for sure: cruising at 120 mph only to be summarily shot down once contact with the enemy is made
However, it has a lot of versatility, good weapon loads, the possibility for easy to make updates in the future with a lot of subtypes (amphibian or pure flying boat with beaching gear, bombs or torpedoes and later in the war cool stuff like radar and leigh light searchlights for spotting U-boats, etc) and would be a blast to fly in multiplayer with a human crew.
It's also challenging in terms of CEM (even today it's not certified to fly with one pilot) and would be a blast to fly in bad weather once the dynamic weather feature is patched into the sim, because for an aircraft that served so much time in adverse weather conditions it used to have some pretty pitiful de-icing equipment. It's a crap-plane extraordinaire with interesting load outs, huge usage in many theaters and multi-crew capability, what more is there to ask for?
It was a true workhorse with a big supporting role in some of the war's most vital aspects (the U-boat threat and battle of the atlantic) and also turned around some engagements that were considered pretty major, either due to tactical/strategic impact or simply due to morale/propaganda value. For example, i think it was a Catalina that spotted the Bismark and enabled the Swordfish to mount their attack that damaged its rudders and rendered it helpless.
Which brings us to the second one, the Swordfish. This is another one of those obsolete aircraft that still managed to soldier on until the end of the war, by switching around its role and making use of its simple to use and maintain nature. This one would be like flying a tiger moth with bombs, it has a fixed pitch prop so CEM would be pretty easy and it also comes in interesting variations and loadouts as the war progresses: floatplane variants for the Mk.I, rockets on the Mk.II, radar on the Mk.III, flying with three crewmen or substituting the navigator/observer for an extra fuel tank, etc.
The swordfish was too a big part of the U-boat hunting forces and that's why it kept serving until the end (there were no 109s in the middle of the atlantic where it operated from "carriers" that were little more than converted merchant ships), it was used during some very high profile, iconic raids and it even took part in the channel dash operations trying to attack the German warships running the gauntlet (with disastrous results, it was what prompted their change of role from anti-ship to anti-submarine).
On another note, both of these types also saw service in the pacific so it's like killing two birds with one stone if they are modeled, three birds if you count the possibility of a mediterranean expansion (taranto raid, Libya raids) etc.
During the Bob timeframe both of these types would probably be used more in coastal command type missions, but i think i read that Swordfish were also active in bombing raids during the Dunkirk evacuation, trying to support the troops on the ground. It also comes with floats too and i'm big fan of anything that can land on water.
For the axis now i'm not really sure what could be added, maybe it's just easier to suggest converting some existing AI-only aircraft into flyables. I would like a flyable He-115 for example and having the Do-17/215 would be awesome too, but i don't know what else could be used in a scenario taking place during the BoB.
The good thing is that these would have an almost immediate practical impact in terms of gameplay, while the catalina and swordfish would need a supporting framework of some sort of specific campaign (maybe requiring use of scripting) for single player or organized online campaign for multiplayer that makes them useful: eg, having an online campaign engine that tracks available supplies, so that it would actually make sense to protect your ships from U-boats, having the ability to rescue pilots ditching in the channel or capturing enemy ones, so that you can return them to your team's pool or deplete the opponent's one when flying online, etc.
I've got loads and loads of ideas about what i'd like to see in the future but most of it is 1942 and onwards. I've been waiting for years for some night fighter action, i'm a big fan of multi-role birds like the Ju88 and the mosquito (superbly versatile aircraft with loads and loads of different missions one could come up with for them) and it would be awesome to be flying combined ops with some mossies and typhoons as the main rhubarb force and a couple of Mustang IIIs as "picket ships" to fly higher, check things out and run some interference if the need arises.
However, all that is a long way off for now, so i'll just stick to my initial suggestions that actually have some relevance to the BoB/BoF timeframe. This is also why i don't want to lose the two-stage prop variants of RAF fighters even if we get the corrected ones for BoB, we already have a big map and they could be still used for battle of France scenarios.
I'll stop here before i get completely carried away and start fantasizing about how i would do a dynamic campaign engine