Board Thread:Theories and Speculation/@comment-31955347-20190528202527/@comment-26636534-20190529225215

It's not just gifting chakra that's the issue. It has to do with merging of the aforementioned chakras. Similar to Hagoromo's chakra being split between Indra and Asura, and then Madara later recombining them to obtain the rinnegan. With the same line of thinking, to get the tenseigan, you would need to merge the chakra of pure Hamura-Otsutsuki descendants with chakra of pure Hyuga descendants. Not only that, a continued production of this merged chakra is needed.

What exactly needs to happen for this merger to occur and be self-sustaining is unknown. Toneri could awaken the tenseigan fairly shortly after implanting Hanabi's eyes, while Madara only awakened the Rinnegan after decades. It's worth noting that in Madara's case, he already had the dojutsu(sharingan) and needed chakra, whereas Toneri had the chakra but needed the dojutsu(byakugan).

So provided there is a sustained amount of Hamura-Otsutsuki chakra for the hyuga in question, from what we have seen awakening the tenseigan will occur. Due in large part to the eventual merger of the two chakras.