This is not a strange thing to think, not at all. I implemented something like this on jbpm 3 once. I added custom tags to the transitions and used the forms on the task to present the INCOMING data. The user then got the choice of transitions and when picked did not take the transition but displayed a form that I configured on the transition. Only after submitting the form, the transition was taken.
I did this without creating custom jBPM classes, but just by reading the process xml from the database.
Personally I would think this could be a very nice enhancement to at least the core of jBPM and in a second step maybe the console (but I do not use that either for end-users)