Valve is looking to offer dynamic pricing on Steam bundles in the future, according to official Steam developer documentation obtained by PC Games N. This means if a consumer already owns games that are in a bundle, Steam will automatically discount that bundle by the correct amount.
"With Steam Bundles, if a customer already [owns] some items in the Bundle, they will pay for and receive only the items not already in their account.," said Valve in the documentation. "This allows the best fans of your series or franchise to 'complete the set' and get a deal on the remaining items in the Bundle."
"Past Complete Packs were sometimes a bad deal for customers that already [owned] one or more of the products in the pack. Either it made bad economic sense for those customers to purchase the pack, or they just felt bad about doing so since it [looked] like they were paying for products they already [had]. The new Steam Bundles system addresses this."
I've run into that issue a few times during Steam sales, notably with games that have extensive DLC. Buying bundles that featured games like Sleeping Dogs, Don't Starve, or Fallout: New Vegas ended up being poor purchasing decisions because of DLC. Also the Star Wars or Bethesda bundles simply wouldn't fly for me, because I own half the game already. The fact that bundles didn't take into account the game that you already owned was perplexing, so I'm glad to see Valve implementing this feature.
The pricing is already live on the Valve Complete Pack and will probably be rolling out to other games soon. In the images above, you can see the difference in price between the bundle when I'm not logged in and when I am logged in. In contrast, the image of the Star Wars Collection shows that the price is $99.99, regardless of how many Star Wars games I already own.
Of course, developers can choose to retain the old pricing structure with the inclusion of "Must Purchase Together" bundles. The idea is those bundles will allow for special editions and soundtrack bundles to continue on without consumers being able to get that content cheaper if they buy them at a later date.