It is very similar to Dianella tasmanica I think the recorded specimen is of the same species. It it doesn't look like any of the Dianella species I know. I haven't noticed Dianella revoluta at these lower slope - deep soil sites but that doesn't mean it isn't occurring there.
... also it had finely serrated leaf margins like Unverified Plant which I should have mentioned (it's hard to take close ups when it gets late at the end of a long weeding day).
Does not look like the D. revoluta planted in my garden, in shady situations. I think the best strategy is wait and watch to see how it develops. There are too many potential garden escapes with strappy leaves, and so far I haven't discovered a good match with serrations on the leaf edges.