AFAIK, with WSL2 systemd will be available, however it will take some time before WSL2 can be fully supported in snapd since I don’t think all the AppArmor patches are applied and there’s also a lack of squashfs support in the kernel meaning you need to use something like FUSE.
Note that WSL2 is significantly different from WSL1, and there is much less work to be done to enable WSL2 with snaps than WSL1 with snaps due to the full virtualized linux kernel.