The Thunderbolt 2 spec is not physically different from the original, but utilizes resources better. The original Thunderbolt has 4 channels (2 up and 2 down) that could carry 10 Gbit/s each independently. The new Thunderbolt uses these in pairs for 20 Gbit/s and makes them bi-directional. That gives these ASUS boards the ability to stream 4k resolution content to up to three 4k UHD displays.
This is just the beginning with the ASUS Z87-Deluxe/Quad. Not only does it have two Thunderbolt 2 ports (supports daisy chaining, DisplayPort 1.2), but comes with some great new features including NFC Express, NFC Remote, Wi-Fi GO!, and Dual Intelligent Processors 4 for easy tuning.
There is currently no price listed for the Z87-Deluxe/Quad, but I am sure it will not be two far north of the current Deluxe/Dual at $314.99.