Personally as much as I’d love to have it, I am extremely doubtful that it will happen, at least this century. Maybe far far in the future, at least after 2150 (that is if there isn’t some new mode of transport by then), but I don’t think that anything beyond SRL East will actually be constructed in my lifetime.
Not sure how you got 30km,
Stage 1: Tallawong to Chatswood - 36km - 5 years construction. Opened 2019
Stage 2: Chatswood to Bankstown - 30km - 2017 start, new section will open in a few months, converted section in 2025) - 8 years
Stage 3: St Marys to Aerotropolis - construction started last year or there abouts finishing in 2026 in time for the airport opening, let’s say 5 years? 23km
Stage 4: Hunter Street to Westmead 24km, construction started 2020, this one will take a decade to do.
Regardless of how you put it it’s 113km in a bit less than two decades.