According to this article on nbl website
1. Marquee rule can only apply to unrestricted players (locals).
2. A further 3 unrestricted (local) marquee players can be signed, with only a portion of their salary counting towards the cap.
To me, this means 100% of any imports salary counts towards the cap, with teams encouraged to spend big on Aussies.
Therefore teams would not be able to spend $500k on one import, leaving only $600k available for the rest of their roster. They would be unable to sign anything but budget imports or even if 1 or 2 Aussies were signed under marquee rules this would count as $150k to $350k towards salary cap, leaving hardly anything for remainder of roster, meaning at best you would have budget imports / players.
In Adelaide's case, after Randle, we would have $800k left for the rest of the roster, which would mean we will have to squeeze in a lot of budget players if we opt to get a marquee player or another stud import