hi all,
For people who don't know me, Elo and I and some other colleagues organised a small workshop in Torun in July 2017 on the cosmology side of GR, with one of the hot questions being whether or not dark energy is just a misinterpretation of forcing an oversimplified (FLRW) family of metrics onto cosmological observations: http://cosmo.torun.pl/cosmotorun17_prog.html We are still far from consensus in answering this question - and ET is likely to play a major role.
I haven't (yet) used ET non-trivially yet, although it's high on my priority list. As I presently understand it, the questions of what is Newtonian vs what is GR vs what is a numerically and analytically reliable calculation are presently a lot less-well resolved than published-paper abstracts often claim. My group's results (all software is free-licensed, see my pdf in the workshop proceedings above and follow the links) favour a quite easy production of the "extra" 16% expansion (scale factor) required at the present epoch to match observations (with an LCDM proxy), by taking structure formation into account. The relevant length scale is close to the standard extragalactic non-linear scale, a few Mpc, established observationally since the 1980s.
Apologies if the following is off-topic, but we have an inhomogeneous cosmology postdoc position available here at Nicolaus Copernicus University with an application deadline of 6 April 2018: https://euraxess.ec.europa.eu/jobs/278463
Cheers Boud