You can always make a suggestion to Garmin at https://www.garmin.com/en-US/forms/ideas/ but I would suggest that a generic coaching plan for trail running events is difficult. For road it is easy “5x400 sprints...” but much more difficult when you start throwing on trails (smooth, technical, wet, rolling) not to mention hills - what grade, how long etc. as every trail type race is different, each has some unique training requirements. Just my opinion.
Meaning there is s lot to gain from even basic guidance. New concept for Garmin would be to know the specific event but who has more insightful data than Garmin.
