Such a big bang approach does not offer the "choice between clearing swap contracts into the current PAI/discounting environment or one that uses SOFR for PAI and discounting" as planned by the ARRC. The change is forced on market participants at a price and with a methodology selected by the CCPs.
Such an approach creates the opportunity for value transfer between market participants and may generate unintended consequences. We have detailed some impacts, potential consequences and open questions in a technical document now available freely on a preprint server.
The document, in the muRisQ Advisory Market Infrastructure Analysis series, is titled
SOFR discounting transition: multi-curve and quantitative perspective.
and is available on SSRN with the reference
Henrard, Marc P. A., SOFR discounting transition: multi-curve and quantitative perspective. Market Infrastructure Analysis, muRisQ Advisory, October 2019. Available at SSRN: https://ssrn.com/abstract=3478769.