I think Stellar Tera is worse off on Serperior than something like Fire or even Dragon. You only receive a +1 boost from Tera Blast, which is worse than that of Leaf Storm’s +2 and lose out on the ability to hit Grass resists or what have you for super effective damage. I believe it’ll certainly see some use on Valiant and Enamorus though.Enamorus and Serperior come to mind first.
I also like to believe that Iron Valiant would make for a good Stellar type option. A lot of fast hard hitting Pokemon or Contrary Pokemon would be ideal for Stellar Tera. You want to use it to counter Pokemon who use it defensively, which is a lot of Pokemon really. Like for example using it to counter Kingambit.