The reasoning is the following. Apart from a NN startup throwing the error, there is nothing in the customer's hand that could reassure him/her that the FSImages is good or corrupted.
Although real full checking of the FSImage is only possible by the NN, for stack traces associated with the observed corruption cases the solution of putting up a tertiary NN is a little bit of overkill. The OIV would be a handy choice, already having functionality like loading the fsimage and constructing the folder structure, we just have to add the option of detecting the null INodes. For e.g. the Delimited OIV processor can already use in disk MetadataMap, which reduces memory consumption. Also there may be a window for parallelizing: iterating through INodes for e.g. could be done distributed, increasing efficiency, and we wouldn't need a high mem-high CPU setup for just checking the FSImage.
The suggestion is to add a --detectCorruption option to the OIV which would check the FSImage for consistency.