I'm honestly a bit fuzzy on exactly how the ATRF will relate to the ITRF from a user's point of view, in particular whether it'll be published as ephemerides or

I'm honestly a bit fuzzy on exactly how the ATRF will relate to the ITRF from a user's point of view, in particular whether it'll be published as ephemerides or a correction applied to ITRF. (Jargon - ATRF: the to-be-defined Australian Terrestrial Reference Frame, ITRF: the International Terrestrial Reference Frame, to which WGS84 is aligned at 10cm level.) Regardless though, people using high accuracy GNSS equipment are pretty much resigned to needing sideband information to actually get an accurate result. This is to account for various physical effects which can't be easily or entirely removed, such as ionospheric phase delays. It can be from a base station at a known location ("differential GPS" or "RTK"), or from a separate commercially available satellite broadcast eg, Fugro G4 or Trimble centerpoint RTX. The latter two actually compute satellite orbit and clock corrections to the broadcast ephemerides, by processing real time streams from a worldwide base station network in real time! The ephemerides aren't something you can download every so often, for high accuracy you need something like a few hundred kB a day for the whole constellation, IIRC.