Well, start up problem is a matter of convenience, it's not a fatal problem, but I just like that my laptop with arch+systemd+systemd-boot starts instantly (3 seconds + 6 seconds for firmware), while bsd on my other laptop starts soo damn slow. (btw slow shutdown pisses me off even more)
Though the real issues with rc are much more serious, and eloquently described here (aka you don't have proper login management, service management, device and policy management, and better in a unified way):
* https://lists.debian.org/debian-user/2018/11/msg00616.html
So let me rephrase my statement, I hope that if they replace the good _new_ rc, they keep the interface as simple. For all I care, it would not have to be exactly the same, but I sure hope it stays as simple. The fact that on FreeBSD, I just need to look at a single text file with an easy-to-read-and-edit format to see what is going on, is one of FreeBSD's greatest virtues, IMHO.
Personally, I never found startup time to be much of a problem, on any OS. But having an init system that automatically restarts crashed services and is able to properly shutdown services including any child process they might have spawned sounds nice.
One thing I do like a lot about the BSD init system is that the interface is a text file with a simple format. I hope when they replace good old rc, they keep the interface as simple as that.