Is it plausible to do trail running as weight loss workout?

Yes: Trail running is an excellent type of exercise and highly recommended. While running, i suggest monitoring your heart rate and vary it between aerobic and anerobic exercise meaning varying your speed from cardio to very fast. This will assist with more weight loss and more healthy stress on your heart.

Yes but caution: You should really build up your strength and endurance with non-trail running first, to establish a baseline of fitness and health. Then, as you increase in strength, start hitting hills and slowly challenge the trails. It's better to work in increments to avoid injury.