I think that it should be a combination of sorts for plugin between the vbulletin way and the wordpress way. One click installation from the admin cp with the browsing advantage of vbulletin.org.
Not sure. But I think we can beat vB.org.
What is skinning going to be like? Is it going to be a nightmare like vbulletin 4.0's skinning system?
No. StyleVars is not true CSS/HTML. Both novice and experienced forum owners and style designers were locked into a very strict, immutable style. It was a design straightjacket.
Or will there be a wysiwyg like skinning system?
No. A WYSIWYG editor would mean that the style is largely set in stone, and only minor changes can be made to details like colors and borders.
The XenForo style is true, proper CSS/HTML. If you already know CSS/HTML, then you're good to go. If not, then rely on the hundreds of style developers who will enter the market. You mentioned Wordpress, so I'll point out that Wordpress uses pure CSS/HTML for their styles and over 10,000 styles have been produced for it so far.
What about security? Will it be more secure than IPB, vbulletin, mybb, phpbb etc?
Windows Me is more secure than phpBB.
Seriously every forum software sets out to be completely secure. However with the framework of XenForo, sanitizing input and output is not just a good design practice, it's built into everything that XenForo does.
I'd suggest a search. There has been a lot of hints and info about how plugins will work, how all of their inputs are sanitized, how the style will feel, specifically
Style Properties. Read that thread and if you
really grasp what it is allowing you to do, you'll realize it leapfrogs every other forum solution out there. If I want to add a new feature to a style or to a plugin, my first step won't be to rip my hair out with the thought that forum admins will have to modify 3-4 templates to get that feature.