Love the video! Note that when pad-stitching the lapels, you should roll the lapel over your finger so the pad stitching has the effect of making the lapel behave - otherwise, it really is just fancy permanent basting!
I like your idea about the split skirt and they did still have split skirts in the 30s too, but I think the looseness of women's trousers has slightly less to do with looking like a skirt than a mix of that they kinda come out of loose pyjamas, (either beach or lounging) and mostly to do with modesty, you didn't want things to cling too closely and suggestively to private parts lol 😆 You notice that the crotch on early to mid 30s trousers are very low, (sometimes almost to the knee) and that the closure is always on the side for women's wear even on garments like riding breeches where otherwise they are practically identical to men's. Its also interesting to bare in mind that there was a trend in early mid 30s men's fashion when extremely wide baggy trousers were the vogue (see oxford bags for the extremest version), whether or not this coincided with slacks entering a wider acceptable range of uses for women and influences its style or not I don't know for sure 🙂