I strongly disagree the shorter period of new versions. Even I suggest 2 year periods.
The one year version-cycle urges the graphisoft to come out efficient amount of new features, to justify the reason of the version change.
And it causes, that the new features are just partly new or little more than half-ready.
The new features needs a complete think-over (and in a one year cycle there's no time to do it).
E.g.: if there's missing a tool, there are 2 possibilities: you can make a new tool or develop the existing. The GS mostly chose the new tool option.
But, as a matter of fact, there are too many tools, yet. E.g.: there would be no need to have 2 separate tools for windows, and doors; or even there's no need to have different object-type elements, also (object, lamp, door, window and even the zone stamp too).
Or there are at least 5 fill-type tools (fill, slab, roof, shell, mesh), and the only difference between them is that they have some extra parameters (the slab equals a 0° roof, a fill is a slab without 3d representation etc.); if the wall should have some scripting possibility, it can serve as curtain-wall also (and in this case, the walls should have endless possibilities, like panelled walls, framed walls - without additional extensions).
The 2 new 3d tools (shell and morph) are both lack of some important features, and none of them are so well refined and sophisticated than the other archicad tools.
A new object oriented scripting possibility (with real web-features and other 3d software-connections) would be a significant development.
The paradigmatic changes, mentioned above, could result a way better software.
And in 2 year periods the version changes would be much more easier. I'm an open minded architect, I'm open to the new features, but the change to the new versions for me, often takes more than a year. For several reasons, I'm using for some projects, the ac16, also; and for most of them the ac17, and for just a few I use the ac18.
And the constant version change has some other disadvantages: even the later versions' pmk is not suitable for the earlier versions. e.g. I wanted to place a 2d drawing from an ac18 project into an ac17 one (I had no time for the version change), and I had to use dwg (and it caused some minor problems, which wouldn't come out with pmk).
Talmácsi, István, architect (AC user since 1997, ac4.5 - now: ac18)