You mean the other companies such as Canon, Nikon, and many other happen to announce, from time to time, cameras months away for their effective presence to the market. But in most cases, they don't do it - and before the official announcement, you have only rumors.
A lens roadmap is OK. Lenses are long-term, products are not replaced often - so a 2-year planning is nothing special/dangerous.
But a camera roadmap has too many side-effects:
- encouraging people to pay more attention to future products than the ones currently on sale. You all know the story, but I'll remind you about the Osborne effect.
- letting the competition know exactly what you're doing (as if they wouldn't...)
- limiting your possibilities to adapt to new conditions (e.g. a new competitor's product), because you promised something in the roadmap and you must stick to it
Openly discussing every detail like you are suggesting, well, if they want every good idea stolen (and possibly hastily patented next day in the morning) by others... I can see e.g. Apple suing Pentax because they patented the brick-shaped cameras
I doubt the Pentax engineers would be able to openly talk with the "we know better" forum users all over the world, anyway