It is not a bad idea, but there are a lot of factors working for the success of on-line simulation games.

For one thing, the immersion factor particularly derives from distinct historic events. Modern day jets are interesting and fantastic in their own field, but the limited warfare they went through is very lacking in terms of immersiveness when compared to the second world war.
The second World War was a sequel to the "war to end all wars" in a much larger scale, millions of soldiers clashing all over the world.
The air battles of these vintage era planes were also spectacular... giant squadrons of aircraft clashing over flak bursting skies.. hundreds of massive and shiny four-engined bombers in formation.. German planes baring in like a spike into those formations... flames in the sky.. planes falling down.. a raging torpedo planes and dive bombers flying through ack firing like flames of armageddon... you can probably understand what I'm saying.

The WWII air warfare has an epic scale which appeals to even the people whose country never participated in the war. This, is something modern day jet-fighters can never have.
Another thing is, the limitations in WWII airplanes have ironically designated the "up, close and personal" aspect of air combat. No on-board radar(well.. AH does have AWACS

), no electronics, no gadgets and devices, and no missiles. The fight depends all on human eyes and skill, and this apparently appeals much stronger to many people than looking through the HUD, reading the numbers and boxes, and pressing the button to release a missile, killing a target 5km away.
...
If a modern-day jet on-line sim is ever to be successful, its going to need a warfare large enough for people decades later to remember it as "an epic struggle.." Thank heaven such a thing hasn't happened yet.