Well in my case I use the Octane 3ds max plug-in, so the product will render the same if the person hoe buys it has the plug-in. I also stress this out in the product description, making note that renders will be different if using other software.
De industry has been working towards a good general standard for shading languish for years, but up until now it remains various options and not all applications support these different options.
I share the concerns about interoperability, there are so many different software packages and different types of shaders and renderers that it is impossible to deliver a product that will work on all packages. For this reason I confine my offers to 3ds max format and FBX + OBJ in order to avoid having multiple application licenses and knowledge for using them.
For the OBJ and FBX formats I use the standard shaders, that usually works well on all major 3d software. It basically assures that corresponding map channels load the applied textures (e.g spec., gloss, diffuse/albedo, bump, etc.), unavoidably render settings then need to be done in the specific host application.
Most artist know this is the condition in the industry and accept that they probably need to do these extra adjustments in their host application (if it is a different one). I think most important part is displaying how things potentially can look (make renders as a reference point).
I think your choice for using Marmoset is a good one because it renders relatively photo real and incredibly fast, also nice is the support for allegorithmic substances, good for game model producers because it allows for visualizing the shaders that will also work in game.
However it does not get same results like a good unbiased path tracer and it is a standalone application delivering only display and no animation tools.
I would love to see it in the form of a plug-in for 3ds max and al major 3D software (would be very nice for mo-graphers).
I use marmoset toolbag mainly for my game products.
For the general models and motion graphics elements I use Octane 3ds max plug-in because I think it's the fastest renderer plug-in available. I'm also convinced that this renderer will be most widely adopted because it support over 21 applications and in next release will probably be the most advanced and fully featured renderer for best price available.
It's also worthy to mention that Octane render is capable of rendering stereoscopic VR content(cube maps)and that it will support light field technology (very interesting technology for VR diplay).
(https://home.otoy.com/render/light-fields/)
