I have same issue w/ 2010 XLT wagon w/ 79k miles. First noticed the issue during a short freeway jaunt during frigid winter weather. At first I thought it was rough road. It quickly worsened & became very noticeable in steering wheel, accelerator pedal, seat & floor - a rotating roughness/vibration as though bearing related. Then, pronounced steering wheel wobble developed...luckily I was near an offramp to get back on suburban surface streets. This all unfolded suddenly w/in about 5-10 miles at about 65 mph. This is an extra vehicle, and I didn't wish to incur a big repair bill at the time so I resorted to only using it on surface streets w/in the city where I live. At speeds around 30 mph in stop/go driving there is no issue.
The UK Transit User Forum has some posts that reference a number of related issues traced to CV joints, driveshafts, half shaft bearings, etc. However, it's a little tough to sort out which of these might apply to a model year 2010-on TC sold by US dealers, as the Transit has been around for a number of earlier generations overseas before it was imported for sale in the US.
The TC is still uncommon enough in the US that I don't have confidence a domestic independant repair shop will be able to diagnose this accurately. So, I finally took it to a respected import repair specialist during warmer months; they freeway drove it to further to a nearby suburb, but could not detect any issue. Now I feel at the mercy of the dealer (with access to TSBs, etc) to diagnose this correctly, but I'm still leary that a service writer on commission will replace both half shafts/front struts/wheel bearings, the steering rack, and any other related steering components and say "Now it's fixed". Sure! If a guy experiments with replacing enough spendy components by trial & error at someone else's expense, he'll eventually solve the problem! So, I'd sure like a better idea about what this issue is before I take it to a dealer.