I think honestly that they do have DNA for two reasons.
1. They took DNA from almost everyone they possibly could. They always said that 'Future Advances" may help solve the case, eg. hinting they had something in the bag, and in the future they will one day be able to get that vital piece of evidence to get a conviction. eg. DNA.
2. a) There has been reports that LCN (Low Copy Number) expert. Dr Jonathan Whitaker has been attending Perth to work on the case. If true, It means they have the 'Stranger' DNA that was reported in the Post newspaper articles on file as evidence, and it is of very little value because its such a useless partial profile that it can at best rule a few suspects out, and do very little else when narrowing down suspects/POI's that share similar DNA structures and markers. You would not bother to get this expert in to do any analysis using the LCN technique which can build a profile from literally just a few cells that can be left from anything including skin or sweat and can be a millionth of the size of a grain of sand and still be analysed by some experts to build an almost complete profile.
2 b) The LCN technique must have only started to be used in 2015. The reports clearly state that WAPOL visted Dr Jonathan Whitaker and then he visted Perth to 'work on the case' if true then he has not had a huge amount of time to build the DNA profile into something that can be used to rule in and out any suspects with absolute certainty. He must have been able to rule enough of the identifying loci in to make a connection to Karakatta, however I thought they made the Karrakatta connection with the DNA much earlier, around 2008, so I wonder if they specifically targetted building a profile to match against the Karrakatta profile once enough markers and loci could be matched between the two profiles. The reports seem to make it a certainty that a connection was made with DNA, although you never know and the link could be a different forensic link and the DNA profile has only recently been matched to Karrakatta and it was just assumed that the they must have been connected because a few loci matched exactly and that narrowed their focus and made them convinced, and maybe Dr Jonathan Whitaker confirmed this for them recently. I wonder how long it takes to crawl the DNA database of almost a million and try and match a near useless profile to all the others in the Database and whether new software needs to be created for this?
I do think the DNA profile that they obtained (The 'Stranger DNA') must have been useless though for many many years and they new of techniques being worked on in areas where they could one day maybe use of the profile that they had obtained, I am surprised it has not been contaminated given just how sensitive the DNA can be when analysed using LCN techniques.