Sounds like a bad idea
Orthotics, can be useful adjunct to care. They can be used to give people biomechanics that they do not have while you were trying to improve them and help to make up for ranges of motion which do not seem attainable.
From the gate cycle we know that after initial contact and loading response the calcaneus should start to evert. The calcaneus will continue to evert until it encounters something (like the lateral heel counter of the shoe). At mid stance it should be fully everted and as the opposite leg comes in to swing, begin to invert. The lateral heel counter assists in the inversion/supination process.
To our knowledge, flip-flops, even if they have an increased arch, do not have a lateral heel counter and therefore will promote further lateral excursion of the calcaneus while the medial longitudinal arch is collapsing (i.e.: midfoot pronation). Go ahead and place your foot into inversion and see what happens to your heel. It’s slides laterally.
It’s also well-established that flip-flops, through flexion of the distal toes and engagement of the long flexor tendons, inhibits ankle rocker. It is often necessary to engage these muscles to keep the flip-flop from coming off. Lack of ankle rocker usually will inhibit hip extension and that can cause a constellation of problems.
Though engagement of the long flexors of the toes will have a partial anti-pronatory effect, this is not enough to counter the excessive heel eversion which is happening.
We generally do not think the flip-flops are a great idea and telling someone that it’s “OK” to wear flip-flops as long as it has appropriate arch support, is silly.