Hi everyone, I've changed my late 2013 logic board with early 2015 logic board, and here are the problems I encountered:
- The trackapd cable is not compatible with the logic board, and even if you have a early 2015 trackpad, it's not going to fit in the case.
- My 2013 keyboard works fine on my 2013 machine, but after I switch the logic board, it somehow doesn't work, I'm not sure if it's because I broke it during the disassembling.
So I bought a 2015 parts machine and put the logic board and every other things in it, then everything works just fine.
For those who still wants to do this, I suggest you buy a 2015 logic board, it's less then 100$ even for i7 3.1Ghz 16g Ram, and find a parts machine, just make sure the keyboard, trackpad and the keyboard side case is not cracked or other serious damage, this might need some luck to get a nice bargain.
Generally speaking, I think it's upgradable, it's just going to take some time. There are still some differences between those two models but nothing critical.