That is a significant problem, particularly in the older drugs that have been on the market for several years. Most of these drugs are not even available through the originating company or industry that actually created the molecule. Aspirin comes to mind. It's ancient, yet it's used primarily now for indications completely separate from what it was intended for years ago.
The difficulty then lies in who's responsible for the clinical trials, who is going to do the research, and where the funding is going to come from for the research. So, yes, it is definitely a problem.
In terms of new medications, I think that should be included within the progressive licence process. As indicated by my colleague, if at the outset, within phase two trials, within that licensing it's implied that off-label use for predictable other uses should be considered, that needs to be in the plan for the continuation of that product so that the evaluation continues.