Does the FAA intend to discontinue domestic flight plans and switch to ICAO-only on October 1, 2015?
The link from your question paraphrases and links to “Flight Service Program Changes,” of which the April 13, 2015 7:49:56 AM EDT revision is reproduced below with added emphasis in boldface.


  Flight Service Program Changes
  
  Recognizing a shift in users’ preferences for automated services, the
  FAA is changing its Flight Service operation to make it more efficient
  and reduce costs. The agency will continue to maintain the highest
  level of safety.
  
  The changes come as general aviation pilots are transitioning from
  traditional Flight Service assistance to more automated and web-based
  tools to obtain services. Through the use of updated technology Flight
  Service is taking the opportunity to eliminate redundancies and
  underutilized services.
  
  “None of these changes will affect core flight service safety
  functions such as search and rescue, emergency services, Notice to
  Airmen (NOTAM) entry and dissemination, and pilot weather reports,”
  said Steven Villanueva, Deputy Director Flight Service, in the ATO's
  System Operations Service Unit. “We are phasing in the changes to ease
  the transition for users,” he added.
  
  On October 1, 2015, the FAA will consolidate Flight Watch services
  into routine flight services inflight frequencies to eliminate
  unnecessary duplication of service and provide greater convenience for
  pilots. These services provide inflight weather information to pilots.
  After that date, these services will be available on the same
  frequencies that pilots use to open and close flight plans and to
  receive updates on NOTAMs or Temporary Flight Restrictions (TFRs).
  Dedicated Flight Watch frequencies will be decommissioned.
  
  The FAA is proposing to phase out legacy Remote Airport Advisory
  Service. Seven of the airports do not meet the Agency's criteria for
  receiving advisory service. Flight Service is collaborating with our
  user groups on possible impacts and will be posting the proposed
  change in the Federal Register for public comment.
  
  The FAA is also proposing to implement flight plan filing for civil
  aircraft exclusively under the format used by the International Civil
  Aviation Organization (ICAO). Flight plans contain specific
  information relating to the proposed flight of an aircraft and
  controllers use them to provide air traffic services. Today pilots
  file flight plans in the U.S. under either the domestic or ICAO
  format. The use of one format will simplify the process and align U.S.
  flight plans within ICAO standards.
  
  General aviation pilots increasingly have turned to automation in
  recent years to file flight plans and receive pre-flight briefings.
  New technology such as ADS-B is providing more inflight options to
  pilots. Flight Service will incorporate the industry's newest
  technologies and reduce or eliminate other functions to create
  efficiencies and value. The changes to Flight Watch and RAA are the
  first in what is anticipated to be a series of right-sizing
  initiatives surrounding flight services provided to pilots.
  
  Send your comments, questions, and suggestions to us and share your
  thoughts and ideas.
  
  Flight Service National Airspace Initiative (FSNI) Frequently Asked
  Questions (FAQ)


The linked FAQ list contains a question similar to yours, quoted below including the boldface from the original. Note the first sub-bullet under Flight Plan Filing that states the intent but does not provide a specific date.


  What changes will be made in the Long Term?
  
  Long term changes are being worked with stakeholders. Increased usage
  of technology and automation and less reliance on human delivered
  services will be considered. These changes include:
  
  
  Emergency Frequencies — Pilots, when in distress and using an emergency frequency (121.5MHz), will be responded to by an Air Traffic
  Control (ATC) specialist with surveillance capability, improving the
  timeliness of emergency handling.
  Flight Plan Filing
  
  
  Increased automation that will provide a pilot numerous alternatives for flight plan filing, modification, activation and closure
  Transition to exclusive International Civil Aviation Organization (ICAO) format for civil aircraft
  
  Search And Rescue (SAR) — Increase automation to include Automated Activation and Closure of flight plans
  Relaying Instrument Flight Rules (IFR) Clearances — Flight Service is working with Air Traffic Control (ATC) to develop alternative solutions to enable pilots to talk directly to an air traffic control facility when requesting an IFR clearance.
  


See also the related Aviation.SE question Will the frequency 122.000 MHz no longer be used for Flight Watch after October 1st 2015?