What happened to mesoporous materials for drug delivery?
I think that research of mesoporous materials for several uses is alive and well.  The link referenced within your question is for an article written in 2008.  Wikipedia has a good, though brief, article on its current research status without respect to medical use in particular:  


  A procedure for producing mesoporous materials (silica) was patented
  around 1970, and methods based on the Stöber process from 1968 were
  still in use in 2015. It went almost unnoticed[8] and was reproduced
  in 1997. Mesoporous silica nanoparticles (MSNs) were independently
  synthesized in 1990 by researchers in Japan. They were later produced
  also at Mobil Corporation laboratories and named Mobil Crystalline
  Materials, or MCM-41.


This is an abstract available from PubMed published in 2007:


  Research on mesoporous materials for biomedical purposes has
  experienced an outstanding increase during recent years. Since 2001,
  when MCM-41 was first proposed as drug-delivery system, silica-based
  materials, such as SBA-15 or MCM-48, and some metal-organic frameworks
  have been discussed as drug carriers and controlled-release systems.
  Mesoporous materials are intended for both systemic-delivery systems
  and implantable local-delivery devices. The latter application
  provides very promising possibilities in the field of bone-tissue
  repair because of the excellent behavior of these materials as
  bioceramics. This Minireview deals with the advances in this field by
  the control of the textural parameters, surface functionalization, and
  the synthesis of sophisticated stimuli-response systems.


One possible competitor for sustained drug delivery is transdermal drug delivery.  It seems that this method, which has been used for centuries, is well established and thoroughly approved by agencies like the FDA in the US.  In the US anyway, approval of new medicine or medical devices happens very slowly, and mesoporous materials seem to still be more in the research phase and may not have the level of agency approval that competing systems have attained.