Thunderbolt is a solution in search of a problem.
Some could argue it's a solution for devices that haven't even been thought up yet due to prior I/O constraints.
Others could argue that it could end up being another niche technology that virtually nobody else adopts.
I've never heard anyone complain about having too much I/O available or too much expandability/connectivity. Being that TB is basically an external PCIe x4 port that opens up a lot more possibilities than USB3 or FireWire could ever dream of, and with TB2 on the way...well...
Thunderbolt in place of expansion slots, though, I don't really agree with since you have to spend hundreds of dollars if you want to add slots via a TB -> PCIe enclosure.