64-bit processors will actually have a huge impact on flagship phones to come, especially regards to future proofing, imo.
The 64-bit support itself won't make an impact off the bat, but in the long term it is a natural step in tech evolution. The smaller size (20nm vs 28nm) itself will mean that manufacturers can cram more into an equivalent space, if only marginally. It will run more efficiently, just as fast if not faster depending on clock speeds, and will open doors pass the 3gb RAM cielling. Its also worth noting that more is not always better, as Apple's A8 chip(which is 64-bit) is clocked at 1.4ghz while still outperforming Qualcomms current flagship 805 processor in the Turbo in single core benchmarks. I love my Droid, but i have to cede credit to Apple for leading the mobile chip game since 2013 when the 5s(also 64-bit) was released. That sets us trailing behind nearly 2 years by comparison. This isn't as much a fault of "able-ness" imo, however, as much as it was the direction both companies were taking; Qualcomm's Anand Chandrasekher was quouted way back in October 2013, when Apple introduces its 64-bit A7 chip, as a "Market thing gimmick."