Will they be available in 10.10 or not?
They will not be included in Ubuntu 10.10. There's nothing about Windicators in the Blueprints for Maverick.
From a developer Q&A:
[20:36] QUESTION: ok, giving you a break from Compiz, what can you tell us about the windicators, and the new decoraters? Suggestion if I may, I love the new theme but if I could adjust the window border/header to fit a darker theme that would be awesome
[20:36] thanks ;-)
[20:37] we do plan to keep working on gtk changes for csd
[20:37] client side decoration
[20:37] it means it will gtk drawing its decorations directly
[20:37] rather than compiz
[20:38] but that's quite some work to do and we will need to think about non gtk softwares
[20:38] so while this work continue it will not likely go in 10.10
[20:38] the changes are often discussed on the ayatana list though
[20:38] so feel free to join them to discuss it with them
In other words, there are complications that will take more time to work out for differing systems.
That's juts taken from a forum post but we're past the feature freeze now. Assuming the design team aren't going to have a repeat of the button-side fiasco, it's just bug-fixing herein.
There are a few technical hurdles (client side decoration must be implemented first), etc.
But by far the biggest issue is that no one has been able to come up with a good use case for them. Believe me, it's not for lack of trying either. You'll note Mark's blog post doesn't even cite particular examples of something that really needs to be a windicator.
This shouldn't be too surprising, as we've never had windicators but have come up with many other solutions to the problems a theoretically good windicator might solve.
For instance, if it's that the window requires some action, it can call for attention (flash in taskbar). If the action is urgent, the window can pop to the front. In both cases the actual text of the window itself provides far more space and context to display what's important than a small icon in the corner would.
So that leaves us with only unimportant and optional things that might exist as windicators. But these are already there in the form of window controls and program menus.