Texture compression should be disabled by default
Runtime texture compression only makes sense if all the textures are uploaded only once so that the expensive compression step never occurs during gameplay. Doomsday's renderer at present cannot guarantee this, so it's better to default to no compression. Nowadays graphics cards usually have plenty of memory for textures anyway (and fast buses to transfer the textures when needed).
Compression could also be made a default if it didn't reduce visual quality (too badly) and was done as a cached preprocessing operation.