Slight, I suspect as am new to these games that SFP 1&2 are not amenable to story telling scripting and as such stories and scenarios may be limited to the space on the first flight screen of a new campaign which for 1280X1024 screen could be just 250 words = 1200 characters. Your opening 4th Reich idea has already used up half the available space!
250 words is not a lot of room to add flesh to the bones of a story, however a campaign split in parts would allow the story to twist and turn and go on to a final conclusion. This idea would require several campaigns to be linked with the choice of the next campaign depending on the result of the previous - and it would enable us to change from, say starting on the European map, to the desert/Israel map, to Nam (which can be used to simulate China, South America, etc.,) and even utilise (with permission) community maps.
Your 4th Reich scenario would probably require a European map and then a simulated US/Canada map.