dont believe everything you read, including this.

i wouldnt say vista is more hardware demanding, esp not to the extent of all the stuff you would read. Anyone you ask whos actually run it on a fairly recent pc (2yrs old) will tell you that. Plus that is only if you want to run Aero UI which in the car is a no brainer, you dont need that in the car so just use the clasic UI which any computer should be able to handle.
Epias will probably still have problems, they barely can run winxp. IMHO epias arent good carputers, just too many sacrafices have to be made.

I also wouldnt say are carputers are more complicated than an average desktop, really is no difference to be honest.

The best thing to do is to just evaluate your specific situation and hardware and see for yourself if it all works for you. Waiting 6-8 months wont change much, nor will waiting for ServicePack X to arrive cause the truth to it all, there is allways going to be someone who has a problem with something no matter what stage windows is in when you adopt it.
At least if you evaluate it now, you know what the issues are (if any) and can look for solutions to them instead of waiting for that magic moment when everything goes perfect which may never come.

just my 2 cents.