I assume they have the requisite licensing. If you are asking about re-using the torment content from SoD then I am not an expert but I believe you are fine as long as the mod is released for free, no commercial gain, normal mod rules.
Wait, that's off-topic. Resources like creatures etc. What I wanted to know is if Beamdog could carry over engine mechanics to their own engine? The answer is not until they buy the license, right?
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But you can always hope for Planescape Torment: Enhanced edition.