Myself here, who is trying to get systemd-cron into fedora.
It is still in my copr, awaiting a review.
You might like to use it.
However, nothing is changing unless you decide to do so on your installation.
This issue is not related to systemd-cron, well, nothing has changed.
systemd-cron (specifically systemd-crontab-generator in it) is a systemd generator which parses the files a traditional cron daemon would, and writes systemd timer and service unit pairs for equivalent cronjobs.
It apparently does support using sendmail just like a traditional cron daemon (haven’t tested it myself though).
It wasn’t working for me after installing the postfix update, but I hadn’t rebooted yet. I restarted cron.service and, after that, my at job test worked. Might save someone a reboot.