It would be a bit of work, but I'd recommend using two of those for each of the positive/negative connections. That should avoid current crowding and equalize the voltage on the cells as much as possible.
I think the main challenge is the lack of hardware (busbars, holders, etc) available. BH is pretty straightforward about what's new and what's not, in my experience.
Maybe not for this build, but it would be nice in the future to use the thick busbars for the pos-neg connections and the less thick wire for the parallel connections, as the parallel connection current should be relatively small.
I think that the shipping difficulties will become more pronounced as the battery prices fall. If LFP cells get to $60/kwh, the economics just won't work to ship them halfway around the world.
It's a different dynamic than solar panels - the value per kilogram is already lower, and doesn't seem...
I got some 66160 bus bars, like these: https://www.alibaba.com/product-detail/Copper-BusBars-for-LTO-battery-yinlong_1600072963755.html
I had to increase the size of some of the holes because the positive terminal is so big, but it worked.
Sure, it could make economic sense, with extreme hypotheticals. I'm not sure how they would make them for $0, unless they have technology they're keeping to themselves.
We could see a dynamic like the wafer/panel assembly split in solar cells that you mention, but I don't know enough about the...
Are you getting four BMS's, one for each module? If not, you'd have to deattach/reattach the BMS leads every time you separate the modules, which might not be ideal. If i were you, i would get four smaller BMS's, to give yourself some more modularity and protection against individual cell failures.
Looks great, and I'm really digging the new busbars. The BMS ground connections are a little on the long side, but I'm not sure what you could do differently with your cell arrangement
to hurry things along, you could make parallel connections with a 1 or 2 ohm power resistor. That would limit the current to less than an amp with 1 volt difference, but it would be much faster than just waiting for them to settle out.
I don't know about joining end to end, but you can look for busbars used for the 66160 LTO batteries, like this: https://www.aliexpress.com/i/4000889743676.html . Or you could call BH and see if they have any bus bars left over that they'd sell you