In version 1.0.0alpha0 they finally make it possible! Child for abstract states? No! But now at least it’s possible to create own fix for it due to new $transitionsProvider, in which you could define onBefore hook. You can change the behaviour depends on state options. Let’s use “abstract” property that is boolean and extend it: to make it possible to add child state here:

$transitionsProvider.onBefore({
        to: state => !!state.abstract
      }, ($transition$, $state) => {
        if (angular.isString($transition.to().abstract)) {
          return $state.target($transition.to().abstract);
        }
      });

basically if abstract param is a string we set it like a target. Example of use:

 .state({
          name: 'abstract2',
          url: '/abstract2',
          abstract: 'abstract2.foo', // redirect to 'abstract2.foo'
          template: 'abstract2'
        })

to cover more complex case we could set it like a function:

 $transitionsProvider.onBefore({
        to: state => !!state.abstract
      }, ($transition$, $state, $injector) => {
        if (angular.isFunction($transition.to().abstract)) {
          return $state.target($injector.invoke($transition.to().abstract))
        } 
      });

and an example for an abstract state with child that is defined by function:

   .state({
          name: 'abstract3',
          url: '/abstract3',
          abstract: function() {
            return 'abstract3.foo'
          }, // Function redirect
          template: 'abstract3'
        })

All code for experiments is available on plunker.