Think "trays". Think of a record-shop's 'tray' concept where disks are stored in a tray configuration.
Shelves, therefore, aren't using their linearity as the first storage limit, but their width can effectively support trays of X-length - you'll figure out safety limits based on shelf width. If you have trays of 100-200 disks, then shelf-storage limits are exponentially increased.
Standard DVD cases are perhaps a half-inch, or the slims can take 4 to an inch. A shelf that's 4-feet long can hold (4x12=48 inches X 4 slim-line DVDs per inch = 192 DVDs, for example.
A tray that's 7-inches wide (wide enough for a commercial DVD to face forward) might hold 150 disks, or 200 or much more. So, that 48-inch shelf can hold 6 trays X 150 = 900 DVDs. Quite an increase.
Shelves with 5-, 6- or 8-levels get all the larger numeric increases.
Reorganizing - inserting new additions - is a matter of inserting a new tray and grabbing handfuls of disks from one tray and moving it to another.
This, by the way, is the path to collector-itis, you realize. Yet, I've never met anyone who buys home-videos that doesn't try to keep them. Therefore, a collection is started. God help the collectors and all other addicts.
Next thing you'll foolishly ponder is, "How can I catalog them so I don't buy multiple copies?" Oh geez... just roll up yer arm and insert the needle!