According to the Egami Blog, Tamron has patented the optical forumla for a 20mm f/2 VC.
This lens would make a very interesting addition to Tamron's recent releases, notably the 35, 45 & 85mm f/1.8 VC primes. A 20mm f/2 prime with VC would compete strongly against the Sigma 20mm f/1.4 Art (and Nikon 20mm f/1.8G ED, for that matter) as many will gladly give up a 1-stop aperture advantage to gain built-in stabilization.
Description of Patent*
* Some specifications have been omitted here due to translation concerns.