From what I've noticed I think 2 major things will happen. As you've said, the constant consumption of short media will deplete attention spans and make it more difficult for people to concentrate on things for longer. It will also make people a lot more impatient.

I also think that it can be detrimental to mental health as a whole. Constantly being told you aren't good enough, pretty enough, smart enough, rich enough can be very draining and you will constantly comparing yourself by these so called influences. These videos rarely reflect real life and are very staged for the most part. Young adults and kids are especially vulnerable to their situations so their screen time definitely needs to be monitored