Follow-up questions include: how gradual was this transition, and are there any sources on how it was received by those affected (the samurai, imperial court, etc.)?
This Wikipedia article gives basic background on the event, but I'd like to know more. Specifically I asked this question because the article says that the motivation behind the shift was stated to be a return to traditional Japanese culture of narrow sleeves and hakama, and I wanted to know whether or not this was true.
Let's begin by looking at the Emperor Meiji in Western style dress in 1873 and a portrait of him in 1880. The Meiji Emperor doesn't look particularly comfortable in the 1873 photoraph--he seems to be slouching and the sword is pointed at an odd angle to his body, rather spearing the floor. The portrait created in 1880 shows him standing in his Western dress with confidence and poise--a very imperial feel to it (of course it was a portrait, not a photograph, but there is a demonstrative change between these two).
I cannot give you an exact point at which the Japanese court transitioned from Japanese dress to Western dress. In fact, it was probably a slow and beleaguered transition that met opposition from various areas of the imperial household and its advisory bodies. Nor, would I guess, that suddenly the imperial household began to only wear Western dress after a certain date. I cannot read Japanese well enough to read the cited article by Osakabe in which you talk about a "return to a culture of narrow sleeves and hakama." I am however a bit skeptical of such a claim.
The transition to western clothing was part of a larger transition to many things western that historians broadly call the "Meiji Restoration /Revolution" (depending on how you think about it). Thinkers and rising statesmen of the late Bakumatsu and Meiji periods were intent on reforming Japan to fit into a world of western power. For politicians, this meant eventually adopting a constitutional monarchy (1890), adopting a modernized military with advice from other countries, implementing forced cultural changes (like restrictions on mixed bathing--or what sort of clothing was appropriate for the peerage and emperor to wear). The difficulty that the modernizers and thinkers faced the most was how to modernize (westernize) effectively, without losing both what was unique to Japan and the country's nascent unity.
Perhaps this is where the point you mentioned above comes into play. Again, I am skeptical that it was a "return" to traditional Japanese wear since they had probably not departed from it before that early stage, but maybe some persuaders tried to argue that there were aspects of "Japaneseness" in the western garb. Perhaps it was part of trying to reconcile the leaders' direction with what was Japanese--in this case, what was Japanese clothing. Bottom line, this transition to western clothing surely took place alongside the other sweeping changes of the Meiji era that sought to imitate, implement, or copy western practices.
Sources:
Changing Japanese Attitudes Towards Modernization, ed. Jansen
Japan's Modern Myths, Gluck
Meirokuzasshi, ed. Braisted
The New Generation in Meiji Japan, Pyle
