Sorry to insist, my legal background may be lacking, but:
1) I am sure that the W3C, while not incorporated, signed its "host agreements" with three universities. So, contracting may not be linked so indisputably with formal incorporation.
2) the ccNSO and the gNSO are structures within ICANN for the purpose of policy-making and in that regard under the ICANN Board for validation. However, they do perform other useful functions for the respective communities without having to refer to the ICANN Board. as a matter of fact, a lot in the ccNSO relates to internal issues.
Nothing would prevent in my view conferring them with a specific role regarding the IANA function, that would not be subject to the Board validation, should we collectively decide to follow that route.
This would seem to me much more bottom up and distributed that creating a single new, different structure for the sole purpose of contracting, with the concerns that some people have. Aren't we too unimaginatively trying to mimic the currant arrangement?
After all, we have not discussed in detail (or I missed it) the composition of the PRT, but my guess is that it would leverage such existing structures. So why not explore doing it also for the agreement part?
B.