From: Montreal, Canada
Since this seems to be a smaller project and part of it has been done already, this might be a good idea as the next project. As long as it covers the main scenarios (XXX Corps breakout, entire 101st/82nd/1st areas), this sounds good. I would highly suggest making this a standalone expansion, though. Many devs are doing this nowadays; it builds up on the current engine (BFTB), but doesn't require owning the vanilla game. This will thus allow sales from people interested in Market-Garden, but who don't own BFTB for whatever reason.
I can see merit in this approach but I also merit in the more traditional approach of requiring the original BFTB game. If we do a standalone then we'll have to do a full set of manuals, a new tutorial and a full set of tutorial movies. These took between four and five months of my time to develop. If we are also to add any new features, then it would be better to avoid what is in effect a duplication of effort. If we require BFTB, then all we need is a What's New manual and a What's New movie. This would be a lot less effort and could mean we get the data content out to you guys a lot quicker.
How about including the original tutorial and movies? You could point that it IS, in fact, an expansion, even if standalone, and that the included tutorial of St-Vith represents the same game system. Don't think the tutorial not being based on Market-Garden should be much of an issue, since it IS after all just a tutorial, plus the extra setting could even potentially be considered a bonus for those who don't have BFTB. Kind of like how COTA has 2 desert maps (post-patch, I know, but same premise) or how some of SSG's games like Battles in Normandy also have the Ardennes Offensive.
From there on, just include an extra 'what's new' movie and section in the manual.
I think this should be seriously considered. For BFTB, it doesn't really affect them either way. However, if it's not standalone, you potentially shut out a lot of people who don't already own BFTB (eg. they like Market-Garden, but don't care about Bulge, or whatever other reason), because the price of both the core game and expansion will be significantly steeper than either one alone. From a business, it sounds like it'd make sense.