Well I don't think there's any substantial information currently to formulate something meaningful, so there can be hundreds of possibilities.
I do think tough that Oda got the inspiration from Japanese history. Wano is essentially the equivalent of feudal Japan and one of the most influential events in Japanese history was the attack of a handful of US ships under the command of Matthew Perry. Japan had isolated itself from the entire world intentionally for centuries and as a result they lagged behind severely. While the world evolved, Japan remained stuck in the feudal age and that became brutally clear when Perry broke the isolation almost single-handedly and made Japan sign a beneficial treaty for the US. In response Japan underwent a rapid metamorphosis to catch up to the rest of the world.
Now Oda described Wano at one point in quite a similar fashion, namely that it was a largely independent country that had enough military force, the samurai, to block out foreign influences like the WG. Now we recently learned that Wano has been taken over by Kaidou and the shogun. Now both of these person are interesting in this perspective. Kaidou uses Smiley and other modern weaponry, like the gas he used on the Minks, with devastating results. Now the parallel with Perry's ships is easily made. The Shogun on the other hand had in feudal Japan a lot of power, but lost it immediately after Japan opened it's borders to the world as he was a relic of the past.
Now we have Oden saying "open the borders" and a shogun who is collaborating with a foreign modern power (Kaidou). If you start drawing more parallels, this could a possible explanation for the Shogun's actions. He feared Oden's ideas would lead to him losing power, so he worked together with an overwhelming force like Kaidou to stop him.
Of course the OPverse is not Japanese history, so the latter doesn't translate directly in the first. I think though that this is where Oda had the overall inspiration from, but what this exactly has to mean is as this point difficult to say. I do have to say though that when I read Oden's last command it reminded me a bit of what WB once said about Roger: that he was waiting for certain people. Now that it has been revealed that Oden was part of Roger's crew, I'm thinking that "open the borders" is connected with that. Both of these statements have a strong aura of vagueness, but you can feel that they're important.