Oh man..you're still stuck with petitions while Motorola has been eaten by Lenovo..
I understand the initial hesitation for unlocking bootloader and flashing a custom rom. It is assumed that custom roms will never be as stable as stock roms and it will keep rebooting,apps crashing..and what not. .
Listen man, moto g 2013 is history long back. If you want marshmallow,unlock bootloader first, unlocking the bootloader of motorola had been one of the easiest and it has great developers. There are plenty of marshmallow roms and after I write this post, I am going to download the updated Nougat rom by
@srisurya95. I have been using it since 28 Sep and its smooth,stable, never had a single random reboot or any wild battery drain. Enter the world of custom roms and forget the official support. Here's the link to the rom.
http://xdaforums.com/moto-g/development/rom-aosp-oms-substratum-moto-g-t3469861