You can already do this fairly easily;

1) Download the SRTM elevation datasource for the region you're interested:

http://e4ftl01.cr.usgs.gov/SRTM/SRTMUS1.003/2000.02.11/

2) Load the .HGT files into PostGIS using raster2pgsql:

http://postgis.net/docs/using_raster_dataman.html#RT_Raster_...

3) Run your queries, relatively simple:

SELECT ST_Value(elevationraster, Point(51.123,-91.123)) FROM elevation_data;