Study material is lacking big time for advanced exam. The official guide for none of VCAP/VCIX exam is available yet. We all understand it takes dedicated time to write a book, review and modify when new version is released. Study material should be dynamically updated as is docs.vmware.com. Of course lots depend upon if this study material will be paid. With cloud/digitalization book writing business model should change.
Moderators Panel should be formed which might include VCDX or VCAP (Double) should be allowed to moderate the content. We all know how popular and effective this group is for any aspiring VCAP6's https://plus.google.com/communities/103910393937429082483. But I noticed very difficult to browse through and more difficult to validate the authority of the comments.