Chip replacement at the SC would be extremely impractical - it's not rocket science but a car repair shop usually doesn't have the tools or staff trained in how to do BGA chip replacements (or deal with possible complications which may arise during a rework). HOWEVER, in this case the solution was obvious, rather than replacing the entire MCU they should have simply replaced the Tegra module, which is absolutely something well within a car repair shop competency. Such repair would be very comparable to the LTE upgrade (which replaces another module inside the MCU), so $500 price instead of $2,500 - and that's at Tesla level pricing (the module itself is much cheaper, for example a
similar board but with more memory and using much newer processor retails at $99).
Whether or not the board would have a larger emmc is a secondary issue, as to do that they might have to re-qual the board and its software, which could be expensive so I'm not sure how the economics of that work out, but even with just a brand new 8GB chip and lowered logging, this $500 repair would go a long way.