Proposal:
Create a Must Support - Choice of Profile Elements
Add Goal.startDate as 0..1 MS with choice of supporting this or Goal.target.dueDate to meet the must support requirement. In such cases, the server SHALL support at least one element, and the client application SHALL support both elements
Rationale:
It is common for patients to develop goals for their healthcare after they have received a diagnosis or begun treatment. For example, a patient may have a specific outcome they wish to achieve, such as reducing pain or improving mobility, or they may have certain values or preferences that they want to be taken into account, such as avoiding certain treatments or procedures.We Agree, for the purposes of patient goals to get out of their healthcare (particularly at end of life), there may be no target date to be set.
Patients' goals for what they want out of their healthcare can be initiated at any time, including after they are made. The timing of when a patient decides on their goals for their healthcare will depend on a number of factors, such as their health status, their personal preferences and values, and the recommendations of their healthcare providers.
Patients' goals for their healthcare may or may not have a target date for meeting them, depending on the nature of the goals and the patient's individual circumstances.
For some goals, such as reducing pain or improving mobility, there may be a specific target date that is used to measure progress and determine when the goal has been met. For example, a patient may have a goal to be able to walk without a cane within six months of starting physical therapy.
In other cases, the goals may be more open-ended or ongoing, without a specific target date for completion. For example, a patient may have a goal to maintain their current level of health or to manage a chronic condition in a way that allows them to live a fulfilling life.
Ultimately, the presence or absence of a target date for meeting a patient's goals will depend on the nature of the goals and the patient's individual situation. It is important for patients to communicate their goals clearly to their healthcare providers so that they can work together to develop a care plan that helps the patient achieve their desired outcomes.
Background
The Pacio project PACIO Advance Directive Interoperability Implementation Guide documents how to represent, exchange, and verify a person’s goals, preferences and priorities for treatments and interventions regarding future medical care. And is derived from US core profiles.
In summary, focuses on improving the exchange of patient-generated health directives between patients and healthcare providers, but does not specify a specific start or end date for these directives. They can associated with specific encounters or episodes of care to provide context and support the exchange of information between healthcare providers and patients.

Please note that we have used OpenAI's chatCPG to assist in answering this question. We review these responses, and the information provided is based on our experience, implementer feedback, and our design choices for US Core.