Let me begin by saying that I’m genuinely happy that this is being worked on. What I’ve seen of @Iain’s @hannoschwalm’s work is very impressive. Before dismissing their work in favor of laplacians (I hope that’s not the intention) I’d really like to see more comparisons between their method and laplacians. And, when it comes to highlight reconstruction, having a handful of methods to chose from is also a very good thing. What works for one image, may not work as well for the next one.
Personally I prefer propagation in most cases. With darktable being an editor known for leaving the control to the user, my dream would be for these two new methods to peacefully co-exist in darktable 4. 
Also, I think samples matter. Areas clipping that should have been close to pure white (puffin bird sample) are usually less complicated and for these I think just creating a nice roll-off in filmic works quite good.
I have stress test image from a small sensor camera (DMC-LX7) that clips in horrible ways that I like to use to test reconstruction. Here it is:
reconstruction_sample_01.dng (9.9 MB). This file is licensed CC BY-NC-SA 4.0.
Below is are crops from the DNG file attached above, underexposed in editor to better show transitions.
RawTherapee’s “Color Propagation” method with “Highlight compression” cranked up does quite well. It propagates false color (radiating from the windows), but I still prefer it over all darktable methods.
None of the current (3.8) methods in darktable do well. This screenshot uses the “reconstruct color” method.