There may be problems using elemental clones to cast shadow clone, not sure if it ever happens in canon, but I think my short comment didn't get across what I was trying to say. Noburi casts a water clone and gives it lots of chakra, then the water clone casts a shadow clone for normal cost instead of triple cost. Were you envisioning a technique hacked water/shadow clone? No one except Noburi would need to do this to avoid chakra penalties.
That's what I thought you meant - and while it's a fair point that Noburi's close enough to unique in this regard (there might be other weird bloodlines with similar issues, but he's likely to be the first in Leaf), my point was more about the exact scenario you've described: I don't see a reason why, if a Water Clone managed to activate the Shadow Clone jutsu, it wouldn't count as a copy of the
clone (not of Noburi). So, just as stupid and sends the memories back to a being that can't benefit from them. So while elemental clones can hypothetically use element-neutral techniques (which the Shadow Clone seems to be), I doubt it'd work to give us any of the special benefits we want from it training-wise.
I'm sure Jiraiya knows at least one elemental clone technique, so he's technically able to test if elemental clones making Shadow Clones send memories back to the original ninja or not, but it's a lot of chakra to burn testing a weird edge case (especially since Noburi still needs to give his clones the chakra they use to activate their techniques).
I would
guess, as it seems to be a straightforward and fair way for it to work, that he pays triple depositing chakra into the clones for them to spend, then they pay standard to activate jutsu (due to clones explicitly lacking their creator's bloodline abilities, so they have normal chakra networks: neither having an expanded chakra pool in their barrels or the extra cost to activate powers). For example, he could pay 150 chakra extra for a clone to then have 50 extra for it to use jutsu with.
