Mj I think that would be an excellent way to get some indication of where the alkaloids originate. The only problem I see is a practical one: holding Pv leaves in the cheek long enough to get effects will be difficult since raw Pv leaves are so incredibly bitter. Like to the point where it burns. PV is why ayahuasca brews taste bad. Caapi only brews actually taste kinda good, some of them really good.
Another possible complication is if DMT is present in the leaves it can be absorbed as well, so distinguishing the effects of the kratom alks from DMT would prove... interesting.
can't argue with this other than to take P. Viridis with an maoi and then follow that with The Kratom grafted P. Viridis with an maoi and then make a mental comparison of the two experiences. That is not very scientific but I expect that a reasonably sensitive person might be able to distinguish differences. A well experienced P. Viridis practitioner would probably be the best person to judge.
At this stage I think a graft experiment is the first logical step to see what growth compares like. I cn't find much on line but that's not much of a surprise. Best regards mj.