I think this has happened too early to really have an effect on the election. Also, this particular shooting will play into either side's narrative, the left on gun control and anti-queer violence, the right on Islamic terrorism, so any effect it would have would probably be a wash.
I agree that it happened too far from the election to have much of an impact, but I disagree about the narrative.
As the victims names are being released, I'm noticing that they were (so far at least) all Latino names. I'd hazard a guess that - at least among Trump supporters and Tea Party types - the right will shed far fewer tears over the deaths of 50 (and counting) gay Latinos. They may offer "prayers," but I'd bet few Republicans will be showing up to the funerals or demanding that we all take a stand against discrimination directed towards the LGBT community.
The gun control thing? The shooter was - until 2:02am this morning at least - a "responsible gun owner" with a license to carry, and the "if only there were a good guy with a gun" narrative falls flat due to the fact that there was an armed police officer there when the shooting began.
The Muslim angle will play out, though it is worth noting that the guy wasn't an ISIS agent. He "pledged allegiance" to them in a 911 call, but if that makes him a member of ISIS, then John Hinkley was really Jodie Foster's boyfriend.