I think he's in the same situation as Sessegnon, we need to see him play every week and develop before we can make a final decision. For a CB he is still really young and if he does well then there is no barrier to him playing for us in the future. I never had an issue with his play in the defensive third, he's aggressive and likes to play out. Even that famous match where he conceded two penalties, both were soft and he played well overall.
The issue with him is that he is prone to abandoning his post and trying to dribble through people, often losing the ball and conceding fouls. The game where Poch put him on at HT and he got sent off immediately after over-elaborating and then two-footing someone is a perfect example. When he got a big chance under Mou away at Norwich last season, he did the same thing, tried to walk into the opponent's half and gave a terrible ball away from which they scored and we drew the game. At our level we cannot accept mistakes like that. Of course we want our defenders to be aggressive and comfortable on the ball, but Foyth too often makes mistakes from simply being daft. This loan is a chance for him to develop his game without the pressure of playing for Tottenham.