Interleaving does try to colocate the interleaved tables by taking advantage of the fact that the underlying SSTable storage sorts the data by their keys. It doesn't however guarantee that a sufficiently large interleave hierarchy of tables will be colocated on the same node(s) due to range splits (each range has a default maximum size of 64MB).

I'm looking forward to the partitioning work being done right now since one could in theory have a top-level (or root) table (with some tenantID) and tenant-specific tables interleaved, then easily partition on the tenantID to have tenancy isolation on all tenant-specific data.