Redis 5.x is stable and mature enough, so it's time to update database/redis port. However, let's keep existing redis 4.x in a separate port, databases/redis4 for the following reasons: backward compatibility at first and for stability as second (redis 4.x will be supported until redis 6.0 will be released).
Thanks for the comment, Mathieu. I've just tried to update the revision and arcanist has failed with Exception Bad origin state 7.
The svn diff -x -U9999 command creates a huge patch, so I don't think I can post it here, so I'm ready to use -U5 in this case.