Rooting without unlocking the bootloader usually involves an unpatched exploit of some kind. An OTA could make you lose root on a permanent basis, and you may or may not be able to flash kernels, which would be an issue for custom ROMs.
Either way, no such method has been posted for the Moto G yet.
My phones: Galaxy Note II SGH-T889V (with LTE enabled
/ ext4 SD card support on TouchWiz ROMs
), Motorola XT-1045 Moto G LTE (TWRP
Previous phones: Nexus S GT-I9020A, Galaxy Gio GT-S5660M (Arpeggiomod ROM
/ Discussion, stock rooted ROM
), Motorola XT-1032 Moto G.
Phones for which I play "tech support" for family and friends: Galaxy Nexus GT-I9250, Galaxy Q SGH-T589R, Galaxy 551 GT-I5510M, LG C-800G Eclypse, Motorola XT-1032 Moto G