Tomorrow, the new suburban rail (Cercanias) line to MAD T4 will be opened, linking it directly to Chamartin (11min) and Atocha (25min) rail stations. Train will run every 30min and cost 2.15EUR. The tracks are also prepared to be shared with high-speed AVE trains once the high-speed rail tunnel between Atocha and Chamartin is finished in 2013, but it will be a branch and not a full rail center in the sense of CDG or AMS. Travellers going to the old T1-T2-T3 will have to take the shuttle bus to the T4 station.
link in Spanish:
IMO this will significantly improve MAD's accessibility and may end up being more popular than the metro (a train every 30min is not enough IMO). It will provide a direct link to the two main train stations (very akward to reach today with metro), where it will link up to long-distance trains and other Cercanias lines, enabling many more people to reach T4 with just one interchange than with the current metro link.
The future HSR link however will be of limited use, IMO. The sharing of the tracks with Cercanias, and the fact that T4 is a dead-end station with only two tracks and limited platform length strongly limits the number of AVE trains that could stop there. It will unfortunately not be a full-fledged rail center like CDG, AMS or FRA, but it is definitely a considerable improvement from the current status.