We've already upped the storage count from 300 to 500 since the svn update. Guilds enjoy the privileges of 1000 guild storage space though if they have a castle. We can consider this storage increase though.
Indeed, many people create merchants and accounts just to store more items, but sometimes really have to consider what are you storing those items for, if they are worth storing. You may want to dig in your storage a bit and perhaps you may find something to get another mil or two sometimes