Microsoft has released an Analysis Services 2012 and 2014 Performance Guide, 111 pages of multidimensional performance tuning goodness.
Is there a future for the multidimensional cube at Microsoft? Sounds like it may stick around for awhile longer.... watch for improvements in SQL vNext.
Performance is important, and not just for improving business processes. Licensing rules for SQL 2014 will probably cause server administrators to try and keep their server utilization at full capacity. Do more with less.
A similar whitepaper exists for PowerPivot and the tabular model in SQL 2012.