Several issues with the "Random Extension 5.x" RFC were only raised after voting started (due to lack of proper discussion):
Make all implemented engines final?
Remove the SerializableEngine interface?
Remove the CombinedLCG class?
Add the pickArrayKeys() method to the Randomizer?
Rename Randomizer::shuffleString() to Randomizer::shuffleBytes()?
Rename PCG64 and MersenneTwister?
Add the Xoshiro256StarStar engine and class?