Great, thanks for seeing that through!
There is nothing to show up, nor any changes needed for darktable. Use exiftool to fix your existing DNG files, or use the updated version of PixelShift2DNG for new ones or to regenerate the previous ones and that’s it.
Edit: I just realized you meant the new functionality @maruncz is working on, sorry. 
When using 16 Bit TIFF from rawtherapee, I wasn’t able to use filmic i.e… Other RAW modules we’re not active either. I assumed this to be an effect of Not using a RAW file.
Strange that you cannot use filmic. Of course, if your file doesn’t contain raw data, a few modules make no sense (any module that works on raw data, like mosaic, raw denoise, etc.) but filmic is not one of those.
That doesn’t mean filmic gives anything usable or makes sense: filmic handles the transition from scene-referred to display-referred, and a TIFF file can be either (I don’t know rawtherapee, but I’d expect its output to be display-referred).
Filmic RGB is transferring my workflow to Display referred? That’s the first time, I heard that. I always thought of filmic as a kind of tonemapping tool.
It does tone mapping. It has to, as it has to fit the dynamic range of the scene-referred image to the range of the display (so 0…x → 0…1). But in addition, it does a log transform (output = log(input).
So it’s not a module you just use for tonemapping. Tone equaliser would be better for that use, or exposition with masking, perhaps others.
(If you want to check what a module expects as input, and gives as output, hover the mouse cursor over its title bar. Or check the manual, I suppose)
I think the better way to characterize this is that filmic ‘takes it out of scene-linear’, or ‘scene-referred’. The final transition to display-referred occurs 1) in the display transform and, 2) in the file export transform. Those two transforms are the ones that are sensitive to the render-for-viewing requirements.
Edit: added alternate scene-* term.
I’m using this workflow occasionally for pixelshift images: On Rawtherapee’s color management, I set the input profile to ‘Camera standard’ (a simple matrix profile), working profile and output profile to e.g. ‘RTv4_Rec2020’, set ‘Tone response curve’ to ‘None’, so things should stay linear, and export in 16bit TIFF. I can open this in Darktable and turn on Filmic RGB just fine, with the expected results, including image metadata. Of course modules, which depend on the raw data before de-mosaic, such as hot pixel removal, will not work, but then this should be taken care of in Rawtherapee in this combined workflow.