You are thinking about currently released products.
Apple will likely be refreshing both iMac lines and the Mac Pro line in September. It is very likely that Tonga Pro and Tonga XT will be in the bulk of their desktops(iMacs and Mac Pros) by years end.
With Apple moving completely away from Nvidia, Tonga Pro and Tonga XT are their only logical choices for their desktop lines going forward this year and next. We will know in September.
AMD would be foolish to base a strategy on one customer's plans a year after product release. I sure hope Apple uses Tonga more - it's a much better GPU than Pitcairn. But I can't imagine this potential design win is the reason for Tonga's existence.