The implementation is indeed a working GitHub sync adaptor. It works well with the caveat that wikis in which a large number of tiddlers are created or modified in a short period of time could exceed the GitHub API limits. This is due to the fact that the core sync mechanism processes each tiddler change atomically, which translate to a separate git commit for each tiddler modification/creation.
The solution would be a rewrite in which we batch multiple changes within a minute or two as a single commit, potentially storing interim changes in IndexedDB to guard against data loss, much as @joshuafontany suggests.