The scheme was a key recommendation of the child sex abuse royal commission and a long-held demand of victims and advocates.

But allowing churches, charity institutions and state governments to decide against being part of it weakens the commitment the Commonwealth says it has towards supporting victims.

The federal government can't force states and institutions to sign up; it can only compel them through public pressure.

South Australia has already opted out but NSW and Victoria have previously indicated they will support the scheme.

It would be safe to anticipate that the ACT government won't need to be forced to sign up to the scheme, given the territory's recent moves to improve abuse victims' legal rights.

Indeed, the Commonwealth could legally force the ACT, along with the Northern Territory, to opt in – but it's unlikely it would need to.

The ACT's Legislative Assembly passed several laws in recent months to improve the rights of those who have been victims of child abuse. This includes a reportable conduct scheme, whereby institutions must report abuse complaints to an independent authority, and new powers for the ACT Ombudsman that will hopefully prevent claims from being swept under the carpet.

In August, the assembly passed legislation scrapping the time limit that prevented historic child abuse victims from suing institutions; this was another recommendation of the royal commission.

The ACT government had waited for a national move on a redress scheme but, at the time, then attorney-general Simon Corbell said it had become clear it wouldn't be established in the foreseeable future.

The ACT must now opt in to the national scheme to continue strengthening the rights and support available to Canberra victims.

There are still questions over the scheme's finer details but it will become clearer where churches, institutions and states stand as the 2018 start date nears.