Hi Steve,
We have had some discussions on the subject over the years. The first such such device was built over 20 years ago and it worked well, but back then there was no general availability of quality prerecorded material. With the R2R revival the interest in such a product reappeared, but never to the point of actually doing it. The market is still very small... we felt we would probably sell 100 of our phono stages for one head pre, so its development was not justified - for us. It would involve mainly the industrial design and interface, but we already have our hands full with other projects.
At this time I have three such units of different vintage in my system, the oldest one due to an upgrade.
Victor