Ultra-precise astrometry with the next generation of radio instruments

We are at the cusp of a generational shift in the power of radio interferometers, with both the SKA and ngVLA planning for exciting new and powerful instruments. These will be used in conjunction with other radio telescopes to provide VLBI with an order of magnitude greater sensitivity. Furthermore, the new frequencies that will be covered will allow enhanced VLBI observations of sources that can only be observed at high frequencies (e.g. various maser lines) or low frequencies (e.g. pulsars slightly misaligned with our line of sight). We have been exploring the implications of these new instruments, as sensitivity alone will not improve over the current astrometric limits - these being systematic. Traditional techniques for differential phase referencing will not be able to significantly overcome the systematic limits, nor extend the current moderate range of frequencies where such methods can be expected to work. Fortunately, new methods such as Source/Frequency Phase Referencing and/or MultiView Astrometry both reduce the systematic limits and extend the range of operating frequencies. Preliminary steps have been taken to confirm that these new methods will deliver on their promise; future applications that make full use of these capabilities will allow for major improvements in the astrophysical understanding of our Universe