Yeah, LG has been good about updates.
What's even more reassuring is that the difference between the G Pro and the upcoming G2 is marginal. S600 vs S800 chipset isn't enough for me to wait til end of August (that is, if any US carriers get it at launch), nor justify paying the forseen $200+ pricetag for a next gen flagship device vs the $99 for the G Pro, which will probably go on even more of a discount once the G2 is available for sale. On top of that, the screens are both 1080p, and I'm not convinced that the new screen LG has developed is going to be worth the money nor the wait over the G Pro. Oh, and the G Pro is 5.5" vs 5.2". I'd like to keep the extra screen real estate.
All of this means that you get high end flagship phone from LG that will still feel like a high end flagship device in 12-18 months from now and given LG's track record, they will support it as such. For those who were early adopters of the G Pro, that means the next phone after the upcoming G2 will be hitting the scenes just in time for their 2 year upgrade. The G Pro for me was an easy choice especially after I saw the leaks of what the G2 had to offer; I didn't feel like I was going to be left behind with an old device in 12 months from now. The G Pro is the best 5"+ smartphone when you take into consideration its specs, price, and alternatives in the marketplace. Only reason why I can see someone not getting the G Pro is they don't have ATT; can't get good reception in their area with AT&T, or just can't afford the plan pricing.
Oh, and by the time KLP releases and becomes established enough to make a difference (specifically app optimization) it'll be far enough into the future that the next gen device gets leaked and I'll be getting a new phone anyway.
TLDR-
Don't worry, G Pro will be supported and it'll still feel like a premium flagship phone even in a year from today.