> PCIe switch is a few dollars if that's cheaper than upgrading your SOC

perhaps you're more familiar with these options than I am, but I see 4 lane PCIe switches are 10x10 mm and maybe they are a few dollars but take more board space, new/larger power supplies, etc so it seems that the costs are more than just a few dollar PCIe switch chip. not sure how many phone PCBs can handle additional 100 mm2 but definitely looking forward to learning more.

[1] https://www.diodes.com/products/connectivity/pcie-packet-swi...

add to the antennas are likely based on best/cheapest efficiency for the available area, then additional antenna would reduce the area for each and require more effort/cost.