Such an approach has a couple of advantages. One needs to get a PID for a collection anyway and the Handle record allows the storage of type values and this is provided by an API, therefore all one needs is at one place. If one prepends the pathes as provided by RDA for the collection API with the prefix of a Handle Service, one gets a generic collection registry implementation, that can be used across different communities and user groups. The only requirement for a user group would be, to have access to a Handle Service. Such a generic implementation also ensures, that the collection data is always based on the data types as already defined in a DTR. And if one has also schemas available at the data type, as with automated schema generation of the ePIC DTR, one is able to control the data provided for creation and modification of the collection and refuse the operation with a qualified error message.
The necessity to distinguish between the collection registry authorization and Handle Server authorization vanishes. This can be both an advantage or a disadvantage and depends on the authorization policies in question.
A disadvantage is the possible overload of the Handle Server. The collection metadata fields are rather restricted in size, and also they should not change too often, because they refer to the whole collection and not to changements in its members. But especially if the membership is huge or changes too often, this traffic can obstruct the Handle Server.
For the membership therefore one could think of a solution by a reference to a digital object in an external repository, which containes then the membership data. This can be determined even at the individual collection level: whether the membership data of a collection is internal or external can be easily distinguished: if it is an array of member items, it would be internal, if it is an identifier string, it would be external. A membership with only one member item is also a list consisting of this only member item. The creation and changement of external membership data needs additional access to that repository of course. There exists already an implementation as a very early prototype based on flask for such a generic collection registry allowing internal or external membership data.
Find a Prototypical Collection Registry for Subdomain 21.T11998 here