Certainly the rout of Choshu and the loss of key figures was a set
back to various reformist activities, but I haven't read enough of
the literature to assert how significant of a contributor this event
was to the destabilization of power within Choshu.
However, certainly had this incident not happened, I do think there
is an idea that Kusaka Genzui would have been alive to perhaps push
the internal control of Choshu over to more liberal hands earlier.
Even so , there are simply too many variables and other parallel
reformist movements that were going on in other parts of Japan to
ignore. To pin the timing of reformation on one even involving one
clan I think is much too simplistic.
I still haven't finished Albert Craig's work, but his work along
with Thomas Huber's gives a good illustration of politics within
Choshu and the conflict between the conservative pro-Bakufu elements
and the liberal pro-Emperor elements. (These works are still both
available in most academic libraries and on amazon.com if someone is
interested in pursuing them. And if so - feel free to ping me should
you develop any summaries you wish to be shared , archived, etc. on
http://red-bird.org/meiji)
Thomas M. Huber. The Revolutionary Origins of Modern Japan --
Stanford Unviersity Press, 1981.
Albert Craig. Choshu in the Meiji Restoration, Lexington Press, 2000.
I have a suspicion that Huber might have made some arguments
regarding the timing of massive changes in the political scene in
his work, but would have to go back and look at this more closely.
As for Ikedaya - there also seems to be little mention of it in
Craig's work or elsewhere. The only reference someone was able to
find after translating some of the Japanese sites committed to
looking at the students of the Shoin jinja (where many of the
younger reformists studied or passed through), is that had Yoshida
Toshimaro not perished in relation to that event, more than likely
he would have been a key political figure in the Meiji government
(as would have others from Choshu).
Hope this is helpful...
S