PlaceHistoryHandler in M3 uses "<prefix>:<place-specific-token>" history tokens.
Having a fallback PlaceTokenizer (with no prefix) would allow both unprefixed tokens and using your own matching instead of GWT's "there must be a colon, and everything before it is a prefix" approach.
For instance, providing only the fallback PlaceTokenizer would allow using any kind of history tokens, provided you do all the matching and "dispatching" from within a single PlaceTokenizer: GMail-style (path-like), Reader-style (query-string-like), Wave-like, etc.
This is less "clean" than allowing a pluggable "matcher/dispatcher" ("I wan't a '/' as separator", "I wan't a fixed-length prefix rather than a separator", "I want to use regexps", etc.), but easier to implement.