The current development build is fully 16bpc - About a decade later than I would have liked but still - that leap has been made.
Also I think it always was the case that internally where it was needed image data is sampled up to floating point space internally to do such calculations.
Personally I think there is a bit of pissing and whining going on with both the FOSS enthusiasts and the Professionals over this. The gimp is neither as good as the former point out or as lousy as the later claim. I use the GIMP in a professional environment. I am not going to pretend that it is as good as Photoshop but given the amount of time it would save for the things I actually need to do I would take a long time for me to break even (I am in Australia so the Australia tax is a significant contributor to that).
If you are doing motion graphics, texture art or digital painting, I would say look at the Krita project (www.krita.org). They are interested in producing a tool for professionals and it has a healthy amount of development going on behind it.