The Haiku logo in the deskbar just looks bad. The leaf is fine, and is also quiteeasily recognizable even if it doesn’t spell out the name.
And the OS has sufficient visual identity without having to put the logo there, really. People will notice that this is not Windows or MacOS and will ask about it if they are interested.
If anything I’d consider adding a text label that says “Menu” or something like that, because some people managed to not notice that this is a menu and commented to me that “it is very strange and unpractical that the only way to access applications is to right click on the desktop and find them somewhere in the disk hierarchy from there” (similar comments from at least 2 or 3 persons). I think using the full Haiku logo would only make things worse in that aspect.