The Aussie series formally unveiled its new-for-2022 regulations in the lead-up to last weekend's Bathurst 1000, centred around a lighter, cheaper, hybrid-ready formula.
As part of the announcement it was confirmed that Ford will continue its support through the Mustang, while an IP deal has been reached allowing teams to use the Chevrolet Camaro body shape as well.
That means there will be at least two makes on the 2022 grid, Casey admitting Supercars is happy enough for a Mustang vs Camaro battle to begin with.
However he also says the unveiling of the rules opens the door for both Supercars and teams to now hold "sensible" talks with new manufacturers that may want to join Ford and GM.
"That work starts in earnest now, in terms of seeing what additional options might be available," said Casey.
"I think, for 2022, I'd be quite happy with a Camaro and a Mustang. I think there's a possibility of an additional brand, but at this stage, I'm not in a position to speculate as to whether or not that will happen.
"In order to kick those conversations off we needed to have something substantial. We're now in a position where our plans and our designs are at a point where we can now go and start to have a sensible conversation, and be able to describe the car in sufficient detail, so that it can be considered by other brands."
Potential targets for the series could be Toyota, Hyundai and Mazda, those three carmakers featuring heavily in an online fan survey Supercars is currently running.
Casey isn't expecting the new rules to prompt a short-term explosion in entries, though, claiming Supercars is "comfortable with a grid size of 24".
There have been 24 full-time entries for the past two seasons, although there is potential for that to grow next year as Racing Entitlement Contracts shift around during the silly season.
There are a number of RECs that could be on the market or on the move, including the Phil Munday-owned entry that was used to run James Courtney at Tickford for most of the season.
Should that leave the Tickford fold, the squad will need to find a replacement REC, given Courtney is already locked in for another season.
Tim Blanchard is widely-tipped to run his own car next year, which will leave Brad Jones Racing a REC short if it's to stay at four cars, while Matt Stone Racing is known to be considering a move to three cars.