How do you know so much about PD's timetables? Is this fact or opinion?
Before the release of GT6, the Course Maker was touted by Kaz and other Polyphony representatives as either being in the game day 1 or added in shortly afterwards. I think it's safe to say that it's fact that they intended it to be released in the first year, given what they told us.
The VGT timetable was on the official Gran Turismo website. It's still there if you go and look under the GT6 features list.
"Over 20 of the world leading companies in the automotive industry have designed special cars for Gran Turismo, celebrating its 15th anniversary. Over the course of approximately 1 year, cars from each company will be provided one by one in the game."
B Spec came a little over a year after release, so after ~14 months the only thing that hadn't been added was Course Maker and a handful of VGTs. We know CM didn't go to plan, and neither has the VGT program. But assuming all the other features did then that was a reasonable 12 month program of support.
That they intended their DLC program to be along the lines of Forza but with more tracks is speculation on my part, but not without some foundation. They stated several times that there was intended to be monthly track DLC. They obviously intended 2+ VGTs a month.
Assuming that they didn't have more to add, I think that would count as being similar to Forza but more track focused. 12 tracks and ~30-40 cars is roughly equivalent to 3 tracks and ~100 cars in my book, or at least close enough not to quibble about.
All I've done is take what we know and put two and two together. Polyphony doesn't want to be tied down supporting old hardware any longer than necessary when there's a new system out, but they want to provide value and support to their customers as well. 12 months seems to be the standard at the moment, and there's reasonable evidence that 12 months is more or less exactly what they originally aimed for.
Put it this way, I don't see anything that was obviously intended to be added to the game after the 12 month mark. They've ended up supporting the game for longer anyway, but not because that was the plan. Both the VGTs and the CM were intended to be in the game and done a long, long time ago.