i don´t know of any plans to release the Vintage 1966 in steel!
I believe a steel 1966 to be a bit unlikely; right now i find it to be very competitively priced towards comparable pieces by other leading brands. And not less nice
Within GP´s portfolio, it´s priced slighty below the average GP and i´m under the impression additions in that area are not exactly required.
A truly limited edition of 20 or 50 units will not affect the price, because doing steel cases in such little series is not more affordable than doing gold cases. A large edition in steel may "kill" the regular model in gold, therefore to me it doesn´t fit that well.
So i don´t see a steel Vintage 1966 for the future.
Which of course is a guess only!