You're right, Ateco have control of Maserati, RAM, Renault and LDV in Australia and last year their sales, combined, stood at 20,014 units. LDV was their biggest selling brand in 2020, with just over 9,000 units, then Renault, RAM and Maserati.
Interestingly, Ateco have control of Maserati, RAM, Jeep and Fiat in New Zealand, so them wanting to take over Jeep, Fiat and Alfa Romeo for the Australian market, seems like a no brainer. I think they'd love to have control of the same brands in both markets. Not sure if New Zealand would ever get the Dacia brand though, as the Duster is already sold there as a Renault.
Bringing in Citroen and Peugeot to the fold, would get all the Stellantis brands under the one umbrella for the Australian market and could see Ateco try and re-establish those brands on behalf of Stellantis. Inchcape have failed miserably with the Citroen and Peugeot in Australia and at least Ateco have history with selling the brands in Australia previously.
And who's to say Opel couldn't be re-introduced either? If Ateco aren't successful in acquiring the brands they're looking at and they've openly said they're on the look out to establish other brands for the Australian market to grow their business, then could we see Opel back here too? And what about SEAT? That one might be a bit harder, Volkswagen Australia are setting up SEAT's sport brand 'Cupra' in Australia next year, so could be stepping on their toes.