Replying to Julian’s non invitation to speculate. There may be a need if not room for interpretation on the basis of the status of the Regulation and its stated aims.
I believe that the coded answer is that HMRC are asking merely the specific question which their international obligations require them to, they are going no further.
From the international perspective, HMRC may not want to imply in their dealings with say the Parisian OECD on CRS, that any unspecified member of a generally defined beneficial class is in fact a beneficiary entitled to receive income or may be construed as being one.
In other words, HMRC are acutely aware of the danger of provoking overwrought deeming provisions over English law in this context. They do not have the power or for that matter the constitutional jurisdiction to override the law of the land, as it has been so aptly described in the Supreme Court. There is a constitutional limit beyond which tax cannot mould the law.
In other terms, if there is or has been no exercise of a discretion to pay income out to them, then the member of the class might not be considered a beneficiary from the point of view of the Regulation.
Let us not forget the whole of the Regulation hangs off the notion of tax liability, not of the law. May I suggest that this technical opening be considered and once considered, taken, as it is one of the few which the professions will be allowed.