I know that not everyone will agree with what I say here, but:
I am fairly certain that speculation that the letter issued by the LDS church applies to all members is misguided. Instead, the letter very clearly applies only to church leaders and then only to leaders whose possible testimony in legal matters stems from situations that arise through carrying out their leadership activities (or at least involve people who are directly under their pastoral care). The key phrase in the letter is "... leaders should not involve themselves in civil or criminal cases regarding members in their units, quorums, or organizations without first ..."
This letter is NOT a general statement about how church members should respond to requests for legal testimony. If it was, legal activity would be impossible (and would have been impossible for many years) in Utah and other Mormon-dominant areas (a situation that is clearly not the case).
So if a bishop (or member of the ward council that the bishop leads), for example, learns legally important information about a member of his ward (a geographically defined ecclesiastical unit) through his leadership activities within the ward, the church is asking that he contact church lawyers. But if another bishop learned of legally important information that had nothing to do with the exercising of leadership within his own ward (something that applied to a member of a different ward, for example), the request to contact church lawyers would not apply.
I can understand why others might interpret the letter differently (the phrase "members" was used in the preface to the reminder of the policy). But the policy itself applies quite clearly, MOO, to only leaders who are who are about to become involved with legal issues involving someone from within their own "flock."
Within this context, I think some of the questions raised here about whether the church is prioritizing its own reputation above the discovery of truth, or whether a church should be allowed to possibly curtail testimony in this manner, are valid. But the instructions of the letter apply to a relatively small group of people with clearly defined (and mostly geographically limited) pastoral duties. They would certainly not apply to most of the LDS people who could provide evidence in the CD/LVD trials.