In addition to the relatively recent appearance of the "port ridge" ( dongle TB device oriented controller), another issue is the active electronics required at both end of the TB cable. There has been only one supplier of both the active filtering and the cables:
http://arstechnica.com/apple/2012/07/why-thunderbolt-cables-will-be-expensive-until-2013/
TB is never going to price match USB 3.0 ( or replace it). It is also a bad mismatch with single drives. Unless there is some data aggregation involved in the system TB doesn't really get deep traction. For example, coupled to a SATA RAID controller is a more natural fit but that also will take you nonlinear than single USB drive like prices.
Mainstream external storage was not the primary problem Thunderbolt was invented for. It is likely to turn out to be only a minor fraction of TB devices even after prices come down.
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Not.
http://www.drobo.com/products/professionals/drobo-5d/index.php
Again not.
http://www.sonnettech.com/product/fusiondx800raidthunderbolt.html
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That is a bit too specific. The intent of TB is to aggregate legacy data traffic that would be sent to PCI-e if this was an internal set up. So one or more PCI-e controllers of legacy data connected to a computer's PCI-e controller. TB just extends that out of the box. The video aspect is more a convenience of a standard port factor more so than anything else. It also gives it something to do while the primarily value proposition gets off the ground.
Tying GPUs to the motherboard also plays into Intel's ( and AMD's ) agenda of fusing CPU-GPU into a single package. TB just "value adds" that proposition.
Docking station is a very good fit to a CPU-GPU based system with limited (or no) PCI-e slots. That happens to be the major direction the overall PC market is going so there is high synergy. But the 'display' aspect of the docking station isn't necessarily a given right now.
