I have reviewed  draft-ietf-rift-applicability from IoT point of view.

The document describes routing in the Fat Tree ( mostly CLOS architecture) applicability. I do not find any impact of this work on the IETF IoT networks.
The document methods and RIFT/Fat trees generally are not used in IETF IoT protocols.  However RPL uses  directed graphs with a different protocol.  I did not see any direct IoT applicability of this document to IoT networks. However,  for larger IoT devices and switches one might extract some ideas out of this document in the future.  Though I don't see direct IoT applicability, I still wish to ask a question to the authors: will they view a root gateway/switch of a IoT  network  to act as a leaf in the fat tree architecture ( example: DC scenario) ?  If so, please consider adding a paragraph on IoT applicability in RIFT.

In general, the document is full of acronyms that might be too familiar with the routing area group ( PoD, TOF, ...), but it will help if the document has a definition of terms section or a pointer to such document in the beginning ; alternately, it can  add the acronyms in the relevant diagrams to understand their usage.