I don't think the trend is reversing - they still seem to be...

I don't think the trend is reversing - they still seem to be signing up people fast, so on track for 7-8% before long.

My assumption for upper limit is 10%+. >20% seems unlikely when your biggest competitive advantage is low-price. Commsec reached >50% I'd guess because they had a large captive market of CBA users, combined with a good website and weaker competitors.

Once above 10%, I think they'll need some additional competitive advantages to continue growing it. At least there are some improvements in the pipeline. They've gotten this far without them.