Look at the naming though - its the same 300 series naming. In all those cases,Intel NEVER stuck with the same series naming for improved chipsets in recent history - Z60 to Z70 series,Z100 to Z200 series.
Each of those chipsets launched with a new CPU line. Using what you said,it the chipset should be named the Z470 and being launching with 10NM CPUs.Intel has NOT released a new HIGHER end chipset without a whole series name change for yonks.
This is apparently being launched for the same line as Coffee Lake. So two new high end 300 chipsets for the same line - that is not usual at all.Don't forget what ASUS said - the Z270 can work with Coffeelake. That means power delivery for the Z270 is fine. Why wouldn't it be fine with the fact a number have massively over-rated VRMs?
So that indicates to me if there is changes to power delivery in the new socket,its obviously NOT for Coffeelake,its for Cannonlake,and that increases the chance that the Z390 is the chipset that has that change.When you look at this logically,it makes sense. Coffee Lake is basically just Skylake/Kabylake with two more cores,released a few months before it was expected,so they adapted the current Z270 to the new socket,since it was quick to do.
Plus,another thing since the Z390 is technically the same series as all the other chipsets,Intel has not broken the two CPU cycle. It has happened before - it happened with the P4 and Core2 also,where the power delivery changed with chipsets which technically could run a Core2 CPU but were designed for the P4. AMD did the same with certain sockets too and so on. It could not be even a case of power delivery in terms of current itself,but the way it is delivered.
For all we could know,the Z390 might be literally the Z370 but with differences to the power delivery and regulation more suited for Cannonlake.
I mean did you even know the P67 chipset could work with P55 CPUs?? ASRock made a motherboard which worked with older CPUs. But the main change to P67 was things like power delivery,etc.
OTH,you might be right,its simply for moar money making opportunities.
But look at this post by Eurocom who are responsible for high laptop reference designs:
http://www.tomshardware.co.uk/intel-z390-chipset-coffee-lake,news-56789.html
A lot of those base reference designs are used by companies like MSI,etc for their gaming ranges.
Having said that only one company can clear this up - Intel. If they did that it would clear up any ambiguity.
TBH,none of us really know where this will go as we are simply speculating it will or will not be supported.