j.t.:
There exist various standards for splays but the skill matter remains critically important.
Even TERPs and PANS-OPs normal operations criteria cannot protect for errant blunders.
Having said that, the more modern birds that automatically input the correct amount of rudder for an engine failure on takeoff, and which are capable of both RF legs and RNP accuracy, integrity, and continuity as low as RNP 0.10, could have RNAV/RNP OEI flight-paths that could eliminate the need for splays. Just linear step-up in 2xRNP containment areas, similar to what is done today for RNP AR missed approach procedures.