For easier usage of variables it would be cool, to have a preview of what value they would have. In the ingest window they could be taken from e.g. the first image in the ingest selection/folder/drive, for other dialogues (renaming, ...) it could be the values from the first or only selected image.
Where filenames or paths are generated, the resulting path could be displayed so one can decide, if the pattern is good to be used or needs to be improved, e.g. when values are missing or tokens are misspelled.
You wouldn't necessarily know data was missing with only one sample, but I do like this idea.
Just noticed I wasn't very specific with my idea.
If you have a look at Jeffrey Friedls Lightroom-Plugins, e.g. Folder Publisher, which uses a custom set of variable tokens he created, it will offer a list of possible variables in different dialogues.
In this list, for most of the variables the values of the last selected picture will be shown to clarify, what the value would look like. It doesn't work perfect, but that might be an issue with Lightroom restrictions.
It might be easier to solve in PM, because it's you that are deciding how it works ;)