So far, what I'm seeing is that the 2080 Ti is and will continue to be an improvement while people still make a value argument regarding what is better: Pay less for 10-series or pay 2x as much for 20-series.

The problem with that logic flow is that it makes valuation fallacies.  Ultimately, people should pay what they can afford but just because something costs 2x more doesn't mean that GPU farms won't acquire 20-series for the meager percentage gains because the gains can and most likely will outpace upfront costs in the long run as well as preventing losses when new opportunities present themselves.

So if I were to replace a $500 1080Ti with a $1K 20-Series card.  I paid $500 more at one time on one day.  From here on out, I gain some arbitrary percentage more in performance as well as power efficiency which matters more or less to different people paying different amounts for energy.  Unless you are on some sort of deadline, it doesn't matter if the 10-series or 20-series ROIs first.  Once they ROI, the 20-series will forever hold the profitability high-ground.  On top of all that, it is just as likely that there could be some unique development that only the 20-series could benefit from.  Some RT specific algo perhaps. 

Now, I'm not going to run out and instantly replace 10-series rigs.  However, I am watching the 20-series market closely as I expect any rational person would.