His comment was that he just wanted (like most people) a pretty simple little thunderbolt 'splitter' to get 2 ports out of one.
Which isn't technically possible (at least, not if you want to keep the word "simple" in there).
A lot of us just want a simple thunderbolt to usb 3.0 hub, or something similar.
If you have a USB3 Mac, then what you want is a regular USB3 hub.
I agree that a TB-USB3 box would be useful - but only to those of us with 2011 Macs with Thunderbolt but no USB3. That's probably too limited a market - and shrinking as the people with deeper pockets upgrade their 2-year-old Macs - for anybody to make an affordable one.
(Personally, I can live without USB3 until I upgrade in a year or so - but the Sonnet box looks far more useful, and will probably still be relevant to whatever I upgrade to).
If you are desperate, you can get a Sonnet Thunderbolt-to-ExpressCard adapter and stick in a USB3 ExpressCard interface. However, that product isn't for you - its for AV people with expensive ExpressCard-based kit who are up the creek since Apple dropped ExpressCard from the MBPs - so you won't like the price.
Yet all the devices coming out are high-end (and in this case, butt ugly) docking stations (this one isn't really a dock though, merely a mashup of crap loads of connectors in a box).
Thing is, there's a large fixed cost to building a box with a TB-to-PCIe bridge and Thunderbolt in/out (plus the punter has got to buy a relatively expensive cable). Once you've done that, it makes sense to throw in all the interfaces you can eat, using regular PCIe-to-USB3/Firewire/Ethernet/SATA controllers.
A few more simple devices are needed, thats what the MAJORITY want, and wont pay silly prices for it.
That's not what Thunderbolt is for. If you want a "simple device" then USB will almost always be a better bet. USB3 is fast enough for anything up to a single fast SSD. Thunderbolt comes into its own when you want something like a SSD RAID set... or a dock with half-a-dozen interfaces running at once.
I suspect that Apple's 'cheap and simple' Thunderbolt-to-Ethernet/Firewire adapters are heavily subsidised - and/or some type of kludge short of a full blown Thunderbolt device - on the basis that Apple needs them to smooth over the removal of these interfaces from the rMBPs.
What you have with the Sonnet dock is a box that turns a Mac Mini or MacBook Air into something more like a desktop mini-tower.