Third-party developers who might be interested in developing civilian aircraft for DCS likely wouldn't bother at all if DCS were restricted to combat aircraft. I'd have to wonder what mysterious critical resource would be diverted away from DCS if these third-parties who would only be here for civilian aircraft are developing those modules for DCSW. I haven't seen a justification as to why DCSW should be arbitrarily denied this genre of flight simulation, especially when Eagle Dynamics themselves have already included civilian aircraft in their description of DCSW as a platform.
This is entirely my personal preference, but what I enjoy the most is online public multiplayer, hanging out with people, getting into formation flights, cross countries, and that sort of thing. DCSW has been the most fun I've had in this context. I've been flying on a freeflight server lately which seems almost constantly busy, and people have a great time, stay logged in for hours on end seemingly every day, and make friends. All without firing a single shot.
So why are they here instead of on FSX? Probably for the same reasons I am.
The biggest problems I have with FSX and X-Plane as multiplayer experience is the lack of consistency between users. We need to own expensive addon aircraft in order to see other players flying them online. There have been many instances in group flights in FSX for instance where I don't have the same $50 airport that everybody else does, and the differing elevations caused aircraft operating out of an airport to land, taxi, and park at different levels. Everybody has different REX themes. Where's the adventure in this? In a DCSW multiplayer server, if I bought the C172 but other people didn't, they'd still see me in the airplane because the external model and audio were patched into the base program. If I didn't buy the C172 but other people did, I'd still see them in their proper aircraft. This consistency extends to scenery, and (as far as I can tell) the weather. Little things like this just make the experience feel that much better in multiplayer for DCSW.
DCSW has other advantages as well, but I'm mostly here for the multiplayer, and I'm quite honestly not doing any civilian flight simming at all because I'm fed up with FSX, and X-Plane doesn't seem to have any sort of drop-in multiplayer the way DCSW does.
As for specific aircraft, I'd easily pay full DCS module price for a glider. We already have racing missions in DCS, so I'd love glider tasks.