Could you please be more specific? First of all, what does "in systemd" mean to you, the code in PID1 or all of the code in the systemd project? What is it that doesn't need to be done in systemd? What would specifically be gained by not doing so, and, most importantly, what are the drawbacks?
I think that many people see the advantages of keeping things separate, such as the possibility to replace parts, but fail to see the disadvantages, such as increased complexity.