It is now clear that Helbrutes are the new entry for Dreadnoughts. Superceding, replacing and eliminating Dreadnoughts completely, the new Helbrutes have the feel of a re-boot to me.
Not withstanding the spelling of Helbrute (which I feel should have two L's in! ...probably copyrighted elsewhere perhaps?), I think that the word "dreadnought" should have been retained. One of the main reasons for this, I feel, is because that is exactly what they are! Indeed, the old legions that formed the core of the veterans of the "long war" were indeed around and remember their old colleagues interred in the coffins called dreadnoughts.
Where did the dreadnoughts cease being dreadnoughts and where were helbrutes born? The older background material certainly correlates with the idea that the interred marines were driven mad by being constantly awake in their dreadnoughts (whilst their loyalist cousins were permitted long rest periods between awakenings to preserve their sanity). So, perhaps helbrutes are just taking this concept a little bit further: a bit more mutated than an old dreadnought -- the new background seems to be pushing this angle: a long time spent insane and inside the warp has produced fleshy and mechanical mutations in excess of even "normal" chaos space marine dreadnoughts.
I'll still be calling them dreadnoughts for a little while myself...