The three primary issues here are: 1) The input devices are on SPI, not USB. Apple's ACPI tables don't provide the GPIO mappings for these things via the standard mechanisms, so the chipset driver won't bind. You then still need another driver for the SPI controller, and there's an out of tree one at https://github.com/cb22/macbook12-spi-driver/ . Longer term, the kernel needs to be able to parse Apple's ACPI tables…
As I've posted before, I am so happy now the Macbook Pro is out because we desperately need help on this issue.