Invention

A rhetoric of wiki will address invention as
topical
collaborative 
A rhetoric of wiki will articulate techniques for invention grounded in the features of the wiki.
A rhetoric of wiki will turn the mechanics of writing on a wiki into heuristics. Creating nodes by creating topics. The need to create in-node navigation.
A rhetoric of wiki will create a set of strategies for entering the text and placing invention.

In looking for a way into considering invention, I made a couple of stops.

Scott on invention
In 1971, Scott et al called for "a perspective, overview, or promptuary scheme" of invention, one which "should serve as a generative theory of rhetoric." This new (then) theory of rhetorical invention was
collaborative. it "takes place in a field of persons interacting, each necessarily form he own perspective at any moment." and by collaborative Scott et al understand the audience as an active part of invention, no passive receiver of invention. "Being an audience - not just being a speaker - is also involved in the process of generating and regenerating one's self..." (231)
situated, historically and materially, and so entailing necessarily points of view
framed in various ways: material, etc.
A rhetoric of wiki will speak to how to organize people - socially, conventionally.

topical writing and invention
Bolter, 1990ish, and topics

: What is new [in hypertext] is that the point of the outline become functional elements in the text ("The Computer as Writing Space," Writing Space).

Wikis partake of most of the features of traditional hypertext (malleability, linking,...) and all the drawbacks (loss of place, need to navigate, need to construct navigation).

The inventional potency of hypertext is the ability of the writers to work in spacial representations of topics - places on the screen - and to make the arrangement of those places part of invention rather than presentation.

The wiki - more than a blog, perhaps more than pencil - doesn't just support /TopicalWriting?, it encourages it by design. Fusing words creates a topical writing space and sets up that space for text writing:
it creates a new topic title, which becomes a link to a writing space
it creates a new writing space for that topic
the topic name can be used as a link any place in the wiki

The need to link and organize topics becomes heuristic.

So a rhetoric of wiki will consider and develop topical invention: the use, creation, and naming of topics.

topics on the fly
Wikis allow writers to make connections between topics and to incorporate topics in text on the fly, by a trick of the topic. Fuse two words and the fusion creates a writing space. Links to the space are automagic: if you use a hot word anywhere in the wiki, it links.

And as the wrier builds up a catalog of topics, more stuff becomes readily available. And once the node is created, it is available on call from anywhere in the wiki - even if writers have forgotten they have created the node.

These two features - instant naming and instant linking - bring inventional potencies to wikis. We have the same possibilities in Storyspace or Tinderbox or other hypertext apps.
But with a wiki, the creation of node and link is so effortless that it allows writer-as-inventor to concentrate on the architecture: architecture by topic.

but things get lost
 Without explicit navigation, topics can get buried, so we need extra navigation and indexing features - which most wikis have.
Recent Changes
Index
Search

However, it also means that writers have to create navigation for pages. This creates a cognitive burden beyond the writing.

burdens
naming topics /TopicNaming?
creating navigation
categorizing topics (if wiki allows it)

Techniques for Engaging Invention
A rhetoric of wiki will create a list of techniques for entering the text and placing invention. ThreadMode? serves as a start, but there are others. For instance,
Readers can
invent within the topic: add to what exists, edit what exists, respond to what exists in ThreadMode?
start a new topic
attached to a wiki word constructed from existing text
attached to a new wiki word

Because wikis are about collaboration, a wiki rhetoric will address
/ContributingToWiki? - how, when, what. /ComposingProcesses presents a start on this. 

/ContributerRoles? - the various roles contributers might play...