As yet I have made no attempt to anticipate when systemd kills plymouth. I can do a fade or something else near the end, but would have to add a tweakable variable to the script so that users could 'tune' the timing to their system. Otherwise it would fade too soon or too late. Every system is different. So for now it just plays until plymouth dies. Without a progress bar, it is only an activity indicator like your recent offering.
If fact, it does have a progress bar (disabled) that could also be 'tuned' to reach 100% just before plymouth dies. I don't mind the tuning. But others will not want to.
