It seems to me that an obstacle to a NEW production is the cost itself including orchestration, choreography, staging, costumes, cast, etc. etc. which cannot imitate the 1970s production as well as the copyright problem. Can finances be found?
Renewal was in 1938. What is the term and content of this renewal? Whether this can be extended would depend on the bill before Congress.
If © is still in effect a financial deal must be made with the executors. Another problem- did the executors agree NOT to give permission to a competing version as long as the © holds? Without knowledge of the contracts, terms of © coverage, etc., we can't judge the problem.
As to the German radio production, I will make a guess that the © is ended for the original as written by Joplin and that the production took place without more than a studio audience, and without costumes, staging or use of any part of the 1970s Tremonisha production (thus at minimum cost). I would also presume that the German performance was on State radio with costs paid by the government corporation. The tape may be obtainable if the proper contact is found.
I can't help thinking of the zarzuela format (set production with singing cast in costume but without the movement or choreography of an opera or play type production and attendant high costs. It might be effective for Tremonisha.