The launchd_xml code is mildly toxic for openlaunchd, it's derived off of the Apple Public Source License codebase instead of the newer Apache 2.0 licensed codebase that openlaunchd derives from.
IMO the ASL is going to be required to get FreeBSD to adopt openlaunchd at some point
Note that the pfsense / outbackdingo launchd did something rather naughty -- it put the xml parser back in pid 1 which was intentionally not there by design at Apple.
tl;dr even if you could convince the FreeBSD devs that launchd is a great idea they wouldn't accept this as-is.
IMO the ASL is going to be required to get FreeBSD to adopt openlaunchd at some point