64-bit support is planned and we have been developing with it in mind for a long time now, but I can’t say when we will actually be able to release this.
I’m also really interested in a 64-bit version of the library and hopefully get a at least 2x speedup of the library. I’m working with 3D mapping and we are converting a lot of textures, a city can have up to 500.000 textures. The conversion process is eating cpu cycles and is really a limiting factor for us.
We are willing to help optimizing the code for 64 bit if you lack the resources.
We've actually now released a 64-bit version of PVRTexLib for the 2.8 release, and it's available to download from our Utilities page. Also it might be worth looking at our fast compressor if you've got that many compressions, whilst the quality isn't always as high as the regular compressor, it often performs quite well, and crucially, unlike the high quality compressor, is now thread safe in the 2.8 library. At least during development it might be a better option, as well as in general for simpler case textures.