Yep, whoever said the 200-500 w/ VC is probably correct. Here's the current one overlaid; there's basically an extra inch or two on the new lens, with a big hump near the mount.
Considering Tamron's lineup, I imagine they would consider a $1500-2000 lens pretty serious
Hump ? Hmmmmm....for a built in teleconverter perhaps ? Like in the 200-400 F4L
Bodies: Canon 6D, 70D, T2i gripped, EOS 5, EOS 100, EOS M
Lenses:EF 24-105 F4L, EF 70-200 F2.8L mkII, EF 100 F2.8L, EF 50 F1.8, EF-S 18-55mm, EF 28-80 USM, EF-M 22, Rokinon 8mm HD Fisheye, M adapter
Other : 540EZ, 320EX, 430EX II, Yongnuo triggers & strobist stuff