Some people are already exploring this idea of "language subset". For example, Dhall (https://dhall-lang.org/ https://dhall-lang.org/) could be seen as a subse

Some people are already exploring this idea of "language subset". For example, Dhall (https://dhall-lang.org/ https://dhall-lang.org/) could be seen as a subset of Haskell, with less features but guaranteed termination!