Facebook is hosting a Developer Garage in Palo Alto on Wednesday, this time called “Roadmap Edition.” Facebook says it will be giving developers a “sneak peak of the Facebook Platform roadmap,” and we’ll be there with all the details.

While we don’t know what changes Facebook will specifically announce this week, we have heard from multiple industry sources that the company has been contemplating changes to the Platform recently that could significantly alter the way applications integrate with Facebook’s “viral” communication channels – the requests, notifications, and feed stories that enable much application distribution and re-engagement today.

Earlier tests that we’ve seen in the wild have included new access points for Facebook’s communication channels on the top menu bar in one case, and a missing bottom menu bar in the other, but these are just small tests and aren’t indicative of any specific site-wide product changes. A post yesterday by VentureBeat goes along with what what we’ve seen from some of the test screenshots, and also mentions that Facebook has been encouraging developers to rely more on getting users’ email addresses directly, instead of relying on Facebook’s viral channels for user communication as developers have since the Platform launched.

Were Facebook to make significant changes to the Platform’s viral channel mechanics, it would be somewhat reminiscent of the spring of 2008, when Facebook substantially redesigned the profile page, removing application boxes, which were then one of the major Platform viral channels, from the profile almost entirely. While last year’s changes caused a big shift in the ways developers thought about designing for application virality (and brought big traffic declines to those developers most dependent on profile boxes), many developers adapted and have since thrived. In fact, 2009 has seen the rise of the Facebook Platform economy to its highest levels ever, primarily through the growth of virtual goods-based games and applications and the underlying payment ecosystem.

So while we’re looking forward to seeing what Facebook announces this Wednesday and in the weeks and months ahead, it’s clear that some developers are nervous about what’s coming down the pipe. Were Facebook to make similarly substantial Platform changes again this year, developers are concerned that it could create broader uncertainty for the Platform ecosystem in the longer term. A “second annual” macro-level change could cause investors to be more conservative with developer valuations (in both the private and potentially public markets) going forward.

We hope Facebook uses this Wednesday to give the developer community a clear sense of the boundaries of what it currently considers stable versus dynamic parts of the Platform API. Facebook has shown before that it has the vision to lead developers through painful change in order to reach a healthier place. However, it also needs to be clearer with developers about what assumptions they can make about viral mechanics going forward.