The sharing of the same workflow sounds like a really good thing. At the moment Revit has the distinct advantage of having a version specifically for structural work that obviously has the same workflow as the architectural version, so users can easily switch between with no loss of productivity, and all data is retained. If the Tekla/ArchiCAD relationship can give the same advantages then it should give a lot of confidence to users thinking of buying either program.
The ideal solution would be a Tekla add-on to enable structural design and analysis directly within ArchiCAD itself, and not have to use an external program at all. I've no idea how feasible this is though.