I have not been keenly following the Investor-State dispute debate with all it's intricacies. But for those interested in the subject a paper by Joost Pauwelyn titled "At the Edge of Chaos: Emergence and Change in International Investment Law" provides a substantive account of issues involved.
This explanation of IIL was interesting:
"Understanding IIL as a multilayered, historical construct, where one historically-situated layer (treaty or institution) gets added to the next, also better explains today’s confusion around the multiple goals ascribed to IIL, ranging from promotion of FDI and protection of individual rights to sustainable development and good governance. IIL cannot be explained by a singular motive, agent or plan, be it BITs as credible commitment to attract sunk investments, BITs as photo opportunities tumbled into by uninformed developing countries, investor-state arbitration as depoliticization of state-to- state disputes or IIL as a dark conspiracy pupeteered by rent-seeking arbitrators and law firms. There is no single creator, plan or deliberate design. Rather, it is large and small steps, influences and interactions which together organically produce IIL. This also explains why recent empirical evidence that BITs only modestly (if at all) contribute to FDI has left most participants unfased and not dramatically influenced the system."