Over at EJIL: Talk!, David Caron and Esme Shirlow comment on the backlash against investment arbitration and international economic law more generally, and say this:
For many, the assumption is that investment disputes, absent an arbitration mechanism, will go to the national courts of host States. This has been proposed in the statements of various non-governmental organizations as well as some States. It is undeniable that all States “should strengthen their domestic justice systems for the benefit of all citizens and communities, including investors”. While such a result may be desirable, there are nevertheless a number of hurdles to be overcome before it is possible. In particular, there is the issue of how to test whether national courts are an appropriate or feasible alternative to treaty arbitration. ...
It's a fair point, but I wonder if it goes the other way as well. When considering whether to include investment arbitration in a treaty, should there be an evaluation of whether arbitration is an appropriate or feasible alternative to national courts? This could be done, for example, in the context of CETA, TTIP, and TPP, before establishing treaty arbitration there.
For that matter, it could also be done for all existing investment treaties. I don't recall the issue being considered in any great detail, or with empirical study; there are just assumptions which have never been tested.