64GB is also the limit of Intels desktop i7 processors. I don't think Ryzen is intended as server processors, so 64GB should cover the target market very well.
Nope. X99 i7s support 128GB and quad channel memory. Most of X99 boards come with 8 slots as well. However the setup is way over-priced, so I'm going to preorder Ryzen on day 1 if available. It just seems like phenomenal value.
Sandy-E to Haswell-E i7's do not officially support 128gb, though there have been reports of it working.
Broadwell-E i7's now officially support 128gb.
All the Xeon equivalents (e5-1650/60,80, etc) support 256-768gb depending on the model, if paired with a consumer board that limit is usually 64-128gb.