Stacking into 3D for sure is a way into the future continuing Moors law a little further. But moving electrons will also here hit limits of thermal dissipation.

So let us watch the field of optical computation! Here photons are carrying the information, thermal effects are much smaller. So going 3D does not pose thermal problems.

Poet's OI will be highly relevant, as in optical computing it will help to convert electrons to photons and back on chip level. 

To be watched: Lightmatter, with strong partnerships to GlobalFoundries and ABC/Google!
Too bad, here we still can not invest...