Doyle and Fricke aren't yet replaced. Excluding Holder, who will continue to slip down the order, Fricke is currently 7th in standings, and two points off 5th place. Doyley faces a tougher situation being 12 points off 7th place. With 4 GP's to go quite a bit can change below the top 3/4 who have a buffer over the rest.
Who has been replaced at this stage, and will remain replaced, is Parnitski and Kubera.
I take your earlier point about the Aussie Quals being tricky, it must be a right pain in the proverbial for the better riders to have to come back here, bring motors/bikes for a one week ordeal involving 4 meetings spread over thousands of miles. Great for fans but very tough on riders and no doubt an expensive exercise, and at the present stage, there are 10 Aussies good enough on our tracks to be viable chances for one of the too few 3 or 4 allocations.
As a number of us have commented on in this thread, the qualifying system has a number of flaws in it and does not assure that we wind up with the best 15/16 riders in the world. Its more of a junket for 2nd and 3rd tier riders than a serious attempt to discern the genuine top echelon of riders. There are more intelligent options, some of which have been bounced around in this thread, but unfortunately, intelligence doesn't seem to be a feature in the decisions of FIM and organizational levels of speedway.