In the government press release, there is a comment from Phil Verster that "This and more will be delivered by the ONxpress team, who proposed service levels that far surpass our GO Expansion full business case and will transform GO Transit into a world class transit system to move the region like never before.".
Obviously there's a bit of salesmanship there, but it's still an interesting comment. If the expected service levels have been increased, I'd expect that does imply the use of EMUs with faster acceleration and faster loading times.
Update from Jonathan English: he's hearing that service frequencies may be as frequent as every 3.5 minutes.