I know this question comes up from time to time, and it's nice to see increased options that don't require a bus to reach.
http://www.getwestlondon.co.uk/news/west-london-news/heathrow-airport-hotel-first-directly-13084037
Current completion date on the Terminal 4 Crowne Plaza/Holiday Inn Express complex is October, so something to keep in mind for those who might need to connect there later in the year. Not sure about the date for the Terminal 2 hotel (owned by Arora, no decision about final branding yet)