I do wonder what this Tenseigan / Tensaigan is like. I don't understand Japanese, but I think Tenseigan means Reincarnated Eye or Heavenly [thingy] Eye. Tensaigan I believe means Genius Eye.
That said, this movie shows how little we actually know about Byakugan. I mean, 2 of the strongest characters in the manga had it, so it must be significant beyond the see-through magic.
Uchiha (with the Sharingan) benefited from the Stone Tablet telling them how to make their eyes stronger. Sharingan has also shown to be special to each individual, with each getting a different ability. But the Rinnegan-wielding Hagoromo's brother Hamura only had the Byakugan. Surely to make their team balanced, there must be a lot more to the Byakugan than we are currently aware of.
Then this Tenseigan thingy came up, which I think is unlocked when someone with Ootsutsuki blood implants another's byakugan. Kind of like EMS. But, EMS was still not the final form, so chances are, Tenseigan may not be the final form of Byakugan either.
I have a theory that Byakugan may have evolved beyond its permanently visible state with Bolt/Himawari. That at least one of them may at some point in their lives develop a doujutsu, and that their story may tell us more.
Naruto Part 1 showcased Sharingan and Byakugan as someone balanced.
Naruto Part 2 powered up the Sharingan, while the Byakugan remained unchanged (apart from Hinata showing some improvements on her eyes)
Naruto Part 3 may well be for Byakugan what part 2 was for Sharingan.