The only real benefits if x64 software are:
1. > 2GB memory allocation per process
2. new registers and opcodes that for appropriately optimized software give a substantial speed improvement, but! This mostly aplyes to FPU intensive applications, a.k.a. multimedia, simulations and scientific applications that do vectorisable operations.
NeoLoader is not such an application, its only part that would benefit from this improvements would be the Hashing and Crypto, but! Its already fast enough and I am not going to change the implementations on my own, its much to easy to fuck something up there and compromise security or cause data corruption, I'll stick to a tested well known library.
And now the downsides:
1. every pointer is twice in size, a.k.a. more memory usage
Live free or die trying!