Some believe the location of the ancient Mallapuri kingdom is in Baglung-Myagdi which was mentioned in the Changu Narayan inscription dated C.E. 464. One notable place in Myagdi is Dana, where foreign travelers saw fascinating houses of Thakali merchants who were assigned to control customs between China and Nepal. Your next shooting location could be in unused copper mines, which were traditionally used by the Chhantyal caste and can provide a unique backdrop for filming.
You can study Tiuri (Impatiens Nimspujaree, Impatiens Balsaminaceae) founded by Botanist Bhakta Bahadur Raskoti in 2011 which could be an ideal topic for your next documentary.