Going back to the North East line replacement trains: there is no public reference to dual gauge capability. It does seem likely however that the NSW State Government's planned XPT/Xplorer replacement will be of a very similar specification to what PTV envisions that it requires for Albury services, so if they do in fact piggyback onto TfNSW's order then it might even be a standard gauge only train.
I think you are mistaken if you think PTV will be able to piggyback onto TFNSW's new regional train. If the new NSW regional train does still do Melbourne and Brisbane services then it will require some kind of sleeper / lie flat seat which will not be necessary for a train only running for 3 and a bit hours each way.
NSW requirements will need to meet 10+ hour travel times. It is likely to be similar to a BR class 800/801/802 with long distance interiors being included in the design along with electric motors, pantographs and a diesel engine range extender. The Albury service only needs a slightly upgraded SG vlocity with maybe a buffet.
I keep seeing references to the XPT replacement contract having the option to be expanded to include the Xplorer services, so perhaps the new (assumed) DMU interiors will be modular enough to accommodate shorter distance services (like the Canberra Xplorer). It would certainly give any tender winner an edge when it came to eventually replacing the Endeavour sets, too.
The 2017 Victorian State Budget appears to fund a study/design work for a long distance Vlocity version anyway.
As for an electrodiesel XPT replacement: we've been over this before. It's an attractive idea but you can bet your bottom dollar that a simple proven diesel-hydraulic drivetrain is going to win out when you've got a competitive tendering process going on, even with stringent acceleration requirements. There are good reasons that the only diesel-electric DMUs around in Australia these days are the Adelaide 3000 class.