Adding indexing to views adds another requirement to the dict implementation:
Yes, that's the proposed change
indexing for sequences at least suggests that access is O(1).
That makes it impossible to use, as an example, a linked list to preserve
The docs for the Sequence abc explicitly talk about situations where index is not O(1), and say that while not ideal, this is valid (mentioning linked-lists by name).
The current existing `dict` implementation does not support O(1) index lookup from a view, (as discussed previously), so a change to linked-lists would not change this runtime O characteristic.