It looks like even if the LG G2 does not get an update from the LG, the developers will still end up coming out with a custom version for it because there is really no reason why the G2 should not be getting the new OS.
It might be old but it looks like it is still strong enough to handle the Marshmallow OS. The Verizon LG G2 was just spotted getting benchmarked and the device was running on the Android 6.0 Marshmallow OS.
The test result showed the LG G2 scoring an impressive score of 2728 with the new Android 6.0 Marshmallow which means it is powerful enough for the Operating System. Now all we need to do is convince the custom ROM developers to actually develop one for the users.
While the LG G2 will not be able to use some fo the features on the new Marshmallow, the update is said to help improve the performance and battery life of the device and that is a good enough reason for an upgrade.