VERY excited to see this. We (and quite a few of our peers who make a living from running forums) have been openly debating and evaluating options since IB came publicly into the picture.
Now that that's out of the way I'd like to kick off the discussion of what professional forum administrators/owners would like to see:
Here's some of mine:
#1 Server optimization and scalability. Seriously. People that make a living from their sites have no qualms shelling out cash for a better product, but the hardware requirements are a BIG issue when you're talking about ongoing expenses.
#2 Image and video gallery that is actually INTEGRATED with the forums. ALL images and video that has been uploaded should categorizable, searchable and should be EASILY organized and reused by the member. Take a look at http://www.plupload.com/ for an upload system that resizes the image ON THE WORKSTATION. This is huge, as most people don't have a clue how to resize an image and get frustrated when their 5 MB image takes forever to upload.
#3 Obviously there should be an easy migration path from existing vB systems. From our particular perspective we need a way to migrate stuff that is using customized GARS templates. There also needs to be some capability to port over other existing content from galleries like Photoplog, Photopost etc. and ::shudder:: vBlog.
#4 SEO. A large percentage of existing money making vB sites use VBSEO. There needs to be some provision for either replicating VBSEO urls or providing automated redirects, or it will be financial (SERP) suicide for a site to migrate.
Developer community fostering and support is KEY. I think there is a major opportunity here for xenforo to coopt a lot of the vB dev community, but in order for that to work, there needs to be a CLEARLY outlined standard for how things will work going forward. IB burned a lot of folks, and they will want to know that they have a future with Xenforo.
I'm sure there's tons more to talk about, but that's it for me for now. Really psyched to see a possible way forward as we have been really REALLY concerned about IB and the huge conflict of interest in having a company that is essentially a competitor in the forum space developing the software that runs our site (we have had ZERO intention of ever upgrading to 4.x at this point). We've been STRONGLY inclined to stop at 3.8.X and go to custom development at that point, having an option is hugely attractive.
James and Susan