If there is something that would make Construct2 complete for me, then it would be a plugin that makes text-heavy narratives like those in visual novels easier to create.
Something that can: easily fetch the script from a text document to display on the screen (maybe from a hash table or such, to show both the lines and name of the speaker? Not sure what is best atm), keep track of already seen text for use in functions like rollback/log (for those who click one time too many and miss some text), and the ability to skip or fast-forward through already seen text.
So far I haven't seen any easy way to create the last two effects, unless I've missed something recently. I think a plugin for something like this would be immensely useful for anyone wanting to include text-based story bits in their games. One can always hope?