@RobbSnow
As suggested contact support we should be able sort that for you, as long as it is done before the release date.
Quote: "But actually I do hope we get to keep both steam and TGC copy as it is with GameGuru and Classic. I know, for now it is told we no longer get access to TGC copy after release, but it might change. I hope it will."
You will only get one copy the one you originally ordered. AppGameKit Classic and GameGuru were different as Steam was added after release and the Steam keys were given to all existing users to ensure everyone got the chance to have a Steam copy. This won't be same as you got to decide upon order.
Windows 10, Intel i7 4.2 GHz, 16GB DDR4, NVIDIA RTX 2060