We have not one but two sources that have confirmed that Sonic Mania will have elemental shields.
One is one of our TSSZ commentors, who mentioned that Studiopolis has a Fire Shield in the GameSpot footage we recently covered.
Our TSSZ representative, SonicRemix, also says that she encountered a Water Shield during her time with the game.
@SSF1991 I can verify this, as they were in the demo. I'm also pleased to say that they function the same way as they did in Sonic 3. =)
— Yoshiller (@RealYoshiller) July 23, 2016
So if you like the elemental shields, then you may like the sound of that.