Dude (or dudette)
Are you really worried about that? Everybody knows LG is not the best when it comes to OS updates despite Android's 18 month upgrade path.
However I can see you have been an XDA member since about a year, so you already know you can root, mod and such, so when LG decides not to update anymore (if any) you can just run custom roms on your LG.
Also you must consider that LG G2 has a somewhat future proof hardware which could take us lots of OS versions into the future, specially considering that Google has decided to lower the hardware specs on Kit Kat, so I assume that would be good if they keep on doing that. Well, that is until new 64 bit CPUs (and ported apps) start phasing out 32 bit CPUs by the end of next year.
My Current Devices: LG G2 32 GB, Samsung Galaxy Note (International Version), Nokia Lumia 900, (backup), Motorola Atrix 4G (GB 2.3.4)*sold*, Motorola Lapdock *sold*, Asus Transformer Tablet, Nexus One Google Phone (retired), Viewsonic G Tablet (retired), Nokia N97 40 Gb *sold*, Nokia 5530 *gave it away*, HTC Touch*died*, HTC Touch Diamond GSM*sold*, Palm Pre GSM*sold*