I also adopted Iavor's very helpful categorization. I have not given any motivations below, as it's too difficult to read everyone's motivations inline. Instead, I give several varieties of "no" votes. Let's debate when someone disagrees with me. (To be clear: "obscure" just means that someone should manually opt in, not that the feature is really obscure.) Module System ============= ImportQualifiedPost: yes PackageImports: obscure NoImplicitPrelude: breaking Notation ======== BlockArguments: yes MultiWayIf: might change LambdaCase: might change BinaryLiterals: yes HexFloatLiterals: yes NumericUnderscores: yes NumDecimals: yes OverloadedStrings: bad for beginners OverloadedLists: bad for beginners OverloadedLabels: obscure EmptyCase: yes PostfixOperators: yes LexicalNegation: yes UnicodeSyntax: yes NegativeLiterals: superseded TupleSections: yes ImplicitParams: obscure ParallelListComp: yes RecursiveDo: obscure TransformListComp: obscure Arrows: obscure ApplicativeDo: breaking QualifiedDo: too fresh MonadComprehensions: bad for beginners NondecreasingIndentation: obscure RebindableSyntax: breaking ExplicitNamespaces: yes Data Types ========== DatatypeContexts: no ExistentialQuantification: yes EmptyDataDecls: yes RoleAnnotations: yes StrictData: breaking GADTSyntax: yes GADTs: obscure Patterns and Guards =================== BangPatterns: yes ViewPatterns: yes PatternSynonyms: too fresh NoPatternGuards: breaking NPlusKPatterns: deprecated Records ======= NamedFieldPuns: yes RecordWildCards: confusing DisambiguateRecordFields: yes DuplicateRecordFields: might change NoTraditionalRecordSyntax: no Deriving ======= DeriveGeneric: yes DeriveLift: yes DeriveDataTypeable: yes EmptyDataDeriving: yes StandaloneDeriving: yes DeriveFunctor: yes DeriveFoldable: yes DeriveTraversable: yes DerivingStrategies: yes DerivingVia: yes GeneralisedNewtypeDeriving: yes DeriveAnyClass: dangerous Class System ============ MultiParamTypeClasses: yes NullaryTypeClasses: superseded ConstraintKinds: yes TypeSynonymInstances: yes FlexibleInstances: yes FlexibleContexts: yes ConstrainedClassMethods: yes DefaultSignatures: yes InstanceSigs: yes ExtendedDefaultRules: might change FunctionalDependencies: obscure QuantifiedConstraints: too fresh UndecidableInstances: dangerous IncoherentInstances: dangerous UndecidableSuperClasses: dangerous OverlappingInstances: superseded Types ===== RankNTypes: yes StandaloneKindSignatures: yes KindSignatures: yes LiberalTypeSynonyms: confusing ScopedTypeVariables: might change ExplicitForAll: yes AllowAmbiguousTypes: dangerous ImpredicativeTypes: too fresh MonoLocalBinds: breaking NoMonomorphismRestriction: debate! PartialTypeSignatures: obscure NamedWildCards: yes LinearTypes: too fresh TypeApplications: yes PolyKinds: yes TypeOperators: yes StarIsType: deprecated TypeFamilies: obscure TypeFamilyDependencies: obscure DataKinds: might change FFI === ForeignFunctionInterface: obscure CApiFFI: obscure GHCForeignImportPrim: obscure InterruptibleFFI: obscure UnliftedFFITypes: obscure StaticPointers: obscure Low Level ========= UnboxedSums: obscure UnboxedTuples: obscure MagicHash: obscure UnliftedNewtypes: yes Macros ====== CPP: obscure TemplateHaskell: TH TemplateHaskellQuotes: yes QuasiQuotes: TH Other ===== Unsafe: no Safe: no Trustworthy: no Strict: no Obsolete/Deprecated =================== CUSKs: no TypeInType: no MonadFailDesugaring: maybe