I don't know if you have any experience in this, but any idea how privacy concious Larian are before releases? If you're an interested developer, could a few words to the right people and a confidentiality agreement help? It's always easier to dev something cool when you get to spend time with the toys before the play school opens.
Very unlikely IMHO: NDAs are fairly unusual for non-staff/contractors outside of very controlled conditions (e.g. play-tasting) and probably both a headache and a risk for both parties; but a bigger problem is likely to be licensing issues with what will be at this stage a developers' tool and a lot of the stuff included has quite restrictive (and expensive) licensing.
Some degree of modding is unofficially supported already as mentioned in
this topic: in short, Norbyte's tools can be used to extract the data archives, convert binary data files to XML format and back and GR2 models to Collada format which are compatible with Blender (v2.79 recommended) and so on. But to reiterate,
this is not officially supported and is absolutely at your own risk, including the possibility of having to start over and re-download the entire game if it goes wrong. Please do not contact support or submit feedback about a modded game!