It is probably in bad form to quote oneself however:
As Flyt3est has indicated, the HHMAG (a group which contained the world-wide great and good of the HUMS community - what a pity the advent of EASA caused its demise) discussed cockpit indication at length.
Because the issue was so complex and in view of the lack (at that time) of the required level of reliability, and the simplicity of the systems (events only - and even those provided on a heuristic basis) - a working group was tasked to consider it in detail. This group made a finding that, for the time being, cockpit indications would only complicate the life of the pilot - not simplify it. It also reiterated that the aim of HUMS was to spot developing faults, clusters and trends in time for them to be addressed on the ground and before they could impact upon a flight.
In common with others, I still have my doubts that cockpit indications provide the answer. Perhaps the problem is believing a primary indication that appears irrational and cannot be confirmed by some other means. It could be that, in these days of digital systems and software control, more effort is required in the provision of algorithms that provide (and indicate) secondary confirmation based upon alternative diagnosis paths.
Jim