VassilevB: Feb 1, 16:30 GMT (2018)
Due to how GOG works the build of the game that is available via Good Old Games is a different one to that which is available on Steam as it is DRM free. In order for the Trump DLC to be made available on GOG we'd need to create a whole new build for the service. Unfortunately there are no plans to do that at this time.
cmclout: And yet, it is now 21 Sep 2018, and the GOG product page for this game still says "Please note: 'The Heavy' and 'Donald J Trump' surgeries will be available at a later date", which is apparently a lie.
I purchased this on 27 Nov 2017 and just installed it. There is no Trump. Additionally, there are no soundtrack files in the game directory. I have a soundtrack on my download page under "Game goodies", but that includes only 8 tracks. Accordigng to SteamDB, the Steam version's Anniversary Edition Content contains a "Black Heron Surgeon Simulator A&E OST Mp3" subdirectory containing 23 tracks.
So yes, we here at GOG are definitely getting screwed by Bossa Studios.
I'm really getting sick of paying the same or more here on GOG (versus Steam) and getting less. Less content, delayed updates, lack of updates, and fewer/lack of DLCs. For example, I've had to purchase several games on Steam because Steam had DLCs for sale that GOG doesn't have (for example, A Hat in Time's B-Side soundtrack, AER's soundtrack, and Firewatch's soundtrack). Some developers may release their games on GOG, but they are clearly pushing or enticing people to purchase from Steam instead.
Which is, of course, understandable, given the fact that their biggest motivation is profit. However, if clear-headed and adequate management is done in these companies, then they should be very aware that this is not a viable long-term strategy for the survival of a company. The lifespan of a company is very short (currently around 20 years and has been steadily going down through the years), compared to that of a human being (currently, the global average is 70 years and is getting higher). So, if they behave as if they are actually serving the consumer (because that's is the initial reason why companies exist at all), then they should take their attitude towards customers into very serious consideration, regardless of the specific distribution platform.
What I'm saying is this: if companies keep mistreating customers, then they will inevitably suffer. It's a matter of time (check out the concept of "tipping point" in the context of complex systems theory).