But I forgot to explain.
These threads never go anywhere because the OP is often short and vague and made with incorrect notions about Japan, whereas those who respond often do so with the same basic level of knowledge about Japan or East Asian Affairs, meaning that what they do is throw vague suggestion in the form of one-liners, not because they're lazy or dumb, but because they don't have the necessary knowledge about the area, which is why 80% of threads about Japan, China or any area that's not American or British Politics, or WWII, often fails to get past page 1. In this case the OP contradicts itself, as one one hand it states that Japan would become a second pole to Europe, but that such a scenario would need a divided and weak Japan.
Now, the thing is, misconceptions aside, Japan not closing up in the 17th century wouldn't mean that Japan becomes another pole of power in the Pacific. The structural powers that always prevent Japan from becoming a local hegemon are still there: China, lack of resources, European rivals, demographics, etc.
Assuming that it is not Tokugawa Ieyasu the one who is victorioius in Sekigahara but that instead the Toyotomi remain as Sesshō and Kampaku, then we might see Japan remain open, which means that Japanese silver, copper, swords and luxury items can flow and that imports can come.
This doesn't mean more commerce with Europe though, but rather more commerce with Asia, as Asia was the first source of products for Japan and the main market in which Japan would trade. Commerce with the Americas and Europe might continue and expand, but Japan was already producing weapons on her own in the early 1600s, so there's only so much that they can take from Europe at the time, meaning that effects wouldn't be felt until several decades later, perhaps in the 18th century.
The technological gap between east and west began appearing in the 18th century and really made a difference in the 19th century, in times of the Industrial Revolution.
Then we have another popular topic: Christianity in China. If the Toyotomi are the ones to take over, or any other Clan, then it's just as likely that Christianity would have been seen as a threat as it is that it would have continued to spread, because in Japan and elsewhere, Christianity was seen as the vanguard of Spanish and European Colonization and a perverse influence, etc. With time, we would see some form of action from the government against the spread of Christianity, unless the Government is directly benefiting from it in one way or the other, like Oda Nobunaga did in the 1580s. That is without mentioning other problems that Christianity faced with Japanese culture and religion, from resistance from local Buddhism to poor management of the Jesuits, lack of missionaries and inability to adapt to some aspects of Japanese culture or adapt doctrine to local beliefs.
