Dear devs,
there is a discussion about a temporal gis extension for GRASS
on the grass wiki.
Feel free to join and make you suggestions how to convert grass in a 4d GIS.
http://grass.gdf-hannover.de/wiki/Time_series_in_GRASS
You can also join the grass irc chat
http://grass.itc.it/community/support.php#irc
and share your opinion with others.
My alias there is huhabla.
Best regards
Soeren