How would you like the command's message to be displayed? Since some NPCs are nameless (and have unknown DOIs), how the command would be designated towards any particular NPC—for the command to return the cooldown time of that NPC in particular—is the question.
Also, while yes, it is indeed a planned feature for the future playerdex update, we're not going to conclude that it's too late for some duck-tape solutions to be applied in the meantime, if a workable scheme is devised for them; after all, it's part of why the /iv command was implemented in its current form—it's achieving what a new playerdex/client update could do more conveniently IMO (displaying the Pokemon's IVs, precisely as they're stored in the database), but the /iv command was feasible to introduce earlier, while the playerdex/client updates weren't at a releasable state.