Kanimbla was to be replaced in 2014, by the Canberra class amphibious warfare ship HMAS Canberra. But Canberra may not be delivered on schedule. Also the Canberra class ships are much larger and so less able to do some of the tasks undertaken by the smaller ships.
One option under consideration by the Australian government is to acquire the UK's landing ship dock RFA Largs Bay (L3006), which is being retired due to UK defence budget cuts. Largs Bay is larger (and more capable) than Kanimbla and would complement the Canberra class ships.
Another option being considered is sharing New Zealand's HMNZS Canterbury multi-role vessel (MRV). Canterbury is smaller than Kaninbla and less capable of providing for heavy amphibious operations, but is more suited to low intensity operations (and much cheaper to operate). The closest comparable Australian ship is the southern ocean patrol vessel ACV Ocean Protector.