Proof-of-concept automatic substitute for Slick's MappedTo, implemented using shapeless' Generic.

GenericColumnType.scala

import shapeless._
import slick.ast.TypedType
import scala.reflect.ClassTag

trait GenericColumnTypeImplicits {
  // This definition summons a column type for a type Pk provided:
  //  - Pk is a case class with a single field of type Underlying;
  //  - Slick can summon a column type for Underlying.
  //
  // It conflicts with MappedTo, 
  // so you'll have to opt out of MappedTo if you opt into this.
  // However, with this definition MappedTo becomes redundant.
  //
  // The code uses a library called "shapeless"
  // that can automatically map between case classes and
  // a generic representation called an "HList".
  // The "Generic" object here has "to" and "from" methods
  // that convert back and forth.
  //
  // Because we have access to the "gen.from" method,
  // we can side-step the problem of not having access
  // to the apply method on a companion object.
  implicit def idColumnType[Pk, Underlying](
    implicit
    gen: Generic.Aux[Pk, Underlying :: HNil],
    tag: ClassTag[Pk],
    tpe: BaseColumnType[Underlying]
  ): TypedType[Pk] = MappedColumnType.base[Pk, Underlying](
    primaryKey => gen.to(primaryKey).head,
    underlying => gen.from(underlying :: HNil)
  )
}