I’m new on the block, but have considerable experience with forum software and server enrironments. I also have a little fleet of WordPress sites, LOL. I haven’t grokked all the bbPress stuff yet, but this is a very interesting topic.
-ck- and paulhawke both made some very good points there.
Based on what I know of other systems, the observation about cacheing is accurate. Also a fairly competent Forum program is likely to become considerable larger than any blog because of the nature of the communications, which is many-to-many, rather than one-to-many. Tts not uncommon for forums to have fifty to a hundred thousand posts. How many blogs do you know like that? Just like WP, it all has to be iterated to do a page generation.
Forums are also very spiky, due to their many-to-many, interactive nature. One post begets another or another five. Other than add-ins, Blogs are effectively document retrieval systems where there is a time disconnect between related events.
For these reasons, I lean toward the idea of either hybrid or standalone development. Another concept would be that the plug-in have either less capabilities or some size limits coded in. Sure people could code around, but they would also be on notice that ‘you may be heading for trouble’.