I’m not certain if it’s still the case, but the announcement earlier this year stated the upgrades were being undertaken with no increase to wholesale costs: https://www.nbnco.com.au/corporate-information/media-centre/media-statements/nbn-plans-to-accelerate-highest-speed-tiers
That’s also not to say that the retailers don’t increase their pricing independent of the wholesale pricing.
I know, right? It would be nice if they just opened up the symmetric plans at a reasonable price instead of paywalling them behind business plans.