I guess this is waiting majority of ArchiCAD community: ArchiCAD version on mobile or tablet. It can be much-much simplified version - something like Sketchup with direct connection to BIMx (or having BIMx as extension). Or even as additional feature to BIMx - "BIMx Sketch". Important to pay attention to ergonomic gesture system. Tools for site survey (connection to LiDAR system?).
Built-in communication tools would be also perfect - exchange comments with anyone - builders, architects, engineers. BIMx messenger or something...
Direct connection to BIM Server CDE.