So, this is far from the first time the idea's come up, but we were talking about it in discord so I figured I'd repeat it here:
Reverse summoning, in contrast with regular summoning, brings physical objects to and from the Summon Realm. It's why Keiko vanishes instead of falling asleep, and why we can bring real gold back from the Pangolins from our arms deal. Someone like Keiko going to the Seventh Path also suggests that, unlike storage seals, reverse summoning is totally fine with moving chakra between dimensions.
Suppose you were Jiraiya, on the front lines, and you wanted the most recent intel from Shikaku but it takes a ninja two days to make it to Jiraiya's position from Leaf. Keiko, in Leaf, could reverse summon herself to the Pangolin ambassador to the Toads and leave the report on the Seventh Path. Jiraiya then comes in and takes the report with him to the front lines. The report thus effectively teleports across the continent in the span of a few minutes.
It gets better, though. I mentioned that it seems like reverse summoning doesn't mind chakra? Well, what if we left a full Wakahisa barrel with the Toads instead of an intel report? Jiraiya could take the barrel to the front lines and distribute it to his ninja, replenishing their chakra after a battle or other draining activity. Noburi could remain over in Leaf, continually draining ninja to fill up another barrel, and then when a barrel is filled Keiko goes to the Seventh Path and delivers it, effectively granting Leaf forces indefinite chakra levels.
This is obviously something we should take to Keiko and Noburi first before approaching Jiraiya, because it's their unique talents that enable the plan in the first place, but with WW4 on the horizon it sounds prudent to bring it up to someone.
