Shark bomb + neurotoxin already existed but only a few players could be using that type of team but mainly they used it a few time (youtubers doing it to showcase random teams in sage). Prior to 5.0, water main was mainly used as a healer support and probably will continue. However, with the buff in shark bomb, I just see it as a shift for people to use water main as a nuker especially with the addition of madara kage summit.

As goes for Fire main, the sealing justu will be still be limited to certain few teams that can benefit from the mystery and the shield mystery will still be the go-to mystery to have as a fire main.