The cost isn't a big deal.
What's needed is some assurance that my site's software will still be updated and fixed in 2017. If XF made a bridge, I'd believe in it and pay whatever they asked. If a 3rd party made a bridge, they'd need to convince me.
A 3rd party bridge has to deal with two...
The point was that big sites prefer specialized software. But I agree, I'd rather have xenforo focus on great forum software than spread themselves thin like IPB.
I believe The Economist, NASA, The White House, and The Onion would rather stick with Drupal than some forum-software CMS, but stranger things have happened.
I understand third party bridges aren't always up to snuff, I personally don't trust them because the developers eventually get bored...
Witnessing the downfall of vBulletin, and with it the software my business has relied on, I'd like to make a plea: don't waste your time aspiring to mediocrity.
A forum software team can create the best forum software, but they're not going to make a better blog than WordPress. Nor are they...