... the tendency I perceive here to see giftedness as an innate, unchangeable attribute is something that bothers me.
There is a difference between innate and unchangeable.
Moving towards identifying children who right now need something different from what's on offer - whether or not they did last year or will next year - and emphasising that everyone can improve their capabilities with hard work and appropriate challenge and support, seems very positive to me.
Some may agree with this and still hold that giftedness is innate; These are not disparate concepts.
An emphasis on closing the gap between services offered and services needed is really what's on the table, not a label.
Some may agree with this and still acknowledge that due to being an extreme minority (1-10% depending upon how one measures), gifted students (especially HG, EG, PG students) are an underserved population, and wish to focus on serving their needs. This does not preclude meeting the needs of all learners. By means of analogy, a group established to raise awareness of lung disease does not imply callousness or indifference to breast cancer or any other concern. Those in a lung disease awareness group ought not to have to apologize for their efforts, nor divert their attention to serving other causes out of an imposed sense of guilt or mistaken priority. Similarly, those advocating for an education which better meets the needs of gifted individuals ought not to have to apologize for their efforts or divert their attention to other causes out of an imposed sense of guilt or mistaken priority.
Frankly, maintaining focus on services rendered and required would be beneficial for meeting the educational needs of all students, not just gifted ones.
Flexible cluster grouping by readiness and ability, regardless of chronological age?