Wouldn't it be the other way around though? Wouldn't DRM-free DLC across platforms *not* being compatible be a result of the Store's changes in the first place?

Meh, only interested in Sword of the Stars: The Pit (and I prefer getting it on GOG) so skipping.

I think it's more a question of not making it incompatible (as Pheace pointed out), everything else is up to the developer, but GOG could certainly expect them to offer the most compatible version available. Whether that's important or not depends on how well the DLC is selling and whether GOG is trying to actually maximize the DLC sales or whether they don't really care and just put the DLC up to please the publishers.

Let's assume GOG releases an indie game that's been featured in a humble bundle before - that's tough luck, because I expect most people who got it with the bundle won't pay another time just to get it from GOG. Then let's assume there's a DLC for this game that wasn't featured in the HIB - this is GOG's chance to sell it to all those people who couldn't be convinced to buy a second copy of the game itself. And that could mean a lot of e.g. $4.99 sales for GOG that they'd probably miss out on if their version of the DLC was incompatible to other DRM-free versions.

Sooner or later I'm going to buy the Dungeons of Dredmor DLCs from Desura (for the price of a standalone game), because they're supposed to work with my DRM-free HIB version. That way, Desura will profit from me being interested in the DoD title, even though I got the base game from another source. Supposing GOG would sell the game and DLC, too, then I doubt it would mean good business for GOG if they, contrary to Desura, made their version of the DLC incompatible or accepted DLC incompatible with other DRM-free versions of the game from the dev.

An uninteresting bundle for me. I already own Sword of the Stars, have no use for Tower Wars (because of Steam-only) and I skipped Sentinel and QRTH-PHYL when they were on Indiegamestand (I don't see me buying them now).

Leaves one game that might be interesting for me, but that's not enough to buy the whole bundle.

An update on Sword of the Stars

Since I had some blue coins left over I decided to take a chance as the DRM Free installer Desura gives you was listed as the same size as the Gamersgate one. I bought the Mindgames DLC, downloaded it, and used the trick to copy the installer somewhere.

I experimented some and got an error trying to install the DLC with the base game. The game did load installing the DLC alone, but I wasn't sure if there would be missing files. What I ended up doing was this:

1. Install the base game using the Desura installer
2. Make a copy of the folder somewhere then uinstall the base game.
3. Take that copy and place it where you want the game to go. For example mine is D:\Games\The Pit
4. Run the Mindgames installer from Gamersgate and point it to the folder from the previous step.
5. Once it installs to that folder the game should be playable.

I make no guarantee with this, but I tested every class and all of them worked. I didn't get any errors running the game either.

So it's more like "Two players who pretend to be heterosexual lovers" or "Two heterosexual players who pretend to be lovers".

Fascinating.

Mystery game has been unlocked. It's fren-ze.