Bushido did get an indirect nerf in G&K, but I don't think that's the end of the world. If Japan does indeed get any kind of change, that change will likely come to the Zero, which is widely derided by the players. A general buff to Fighters (giving them more utility, for instance), would set Japan up nicely to continue to dominate air space.
I also think Bushido is a very poor ability. It works good to defend and attack in early game but is useless later on.
Uhhh....no. Bushido truly shines in Japan's AIRFORCE, which is definitively late game. The fact that your great war bombers continue to trounce cities even after they've been at it for a while is thanks to Bushido. Bushido is not at all useless in the late game. (But it's not as useful as in Vanilla.)
You also mentioned that Japan should get a technological bonus, but that is a very modern view of Japan. Japan historically was behind the times technologically, leading to Comdr. Perry of the United States cowing the Japanese government by using his advanced cannon ships in the mid 1800s. The Japanese Shogun realized Japan was so far behind in technology that they were no match for western powers, and even after a reactionary revolt restored the Emperor, even THAT government realized Japan needed to make up that ground. Japan rapidly industrialized (i.e., caught up) in the very late 1800s, leading to their surprising victory over Russia in 1905. Japan has only been a remarkable production civilization for about a century of its existence, and has only been a world technological leader since the mid 20th century.
tl:dr: A long view of history says a militaristic Japan makes more sense.
Well, there were some ruling empresses, hundreds and hundreds of years ago. They're hardly notable compared to Tokugawa Ieyasu or the Meiji Emperor, though. (Of course, they didn't go with either of those for Civ V. They went with Oda Nobunaga, who never ruled the country.
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Reading your posts, you have knowledge of Japanese history - but I think you're very much underselling Oda Nobunaga, who is easily one of Japan's most notable and greatest leaders. Oda, along with his mentee, Toyotomi Hideyoshi, and his rival/ally Tokugawa Ieyasu, are known as the "Three Unifiers" of Japan are viewed as the fathers of the county. Were it not for the unification war launched by Oda to centralize power in Japan, Japan would have likely remained fractured between rival warlords for decades, if not centuries. Given how fractured Japan was during the warring states era, the expansion shown by Civ5's intro screen before his death is truly impressive.
The power of the Tokugawa Shogunate was fostered on the strong foundations laid by Oda's unifcation the warring clans under his control. Tokugawa could never have completed the unification of Japan is Oda and Toyotomi had not left him the tools to do so.
tl;dr: I love Japanese history. Oda's a fine choice as leader.