The idea of the Heresy era dreadnoughts has been around for a while:
http://karichristensen.com/artarchive/artarchive/9193792?originalSize=true
That's from a Horus Heresy artbook (and series of collectable cards IRC), there were also some similar models in the Epic range an looong time ago.
As for quality, the Contemptor is stronger, more heavily armoured and even has it's own force field. Weapons wise it's pretty much identical to the modern dreadnoughts (not ironclads though) and implied they have additional secret stuff.
As far as i know the company line is still that they can't create anything new of this complexity. Beyond maybe, after millenia of work realising that that that turrent was made to take a different but similar sized weapon all along. The only source of new stuff is recovered STC blueprints, currently the contemptor class dreads are better and completely irreplaceable.