One of the stakeholder groups you may not think of right away to include when you prepare your list of stakeholders to draw from for your projects, are Subject Matter Experts (SMEs), especially outside the business teams inside the organization, or experts outside the organization.
It is common for the larger enterprise customers to have Enterprise Architecture Teams with experts in areas such as Security, Usability etc. Software firms may have Advisory Boards advising them on a solution or the product they are building. Such SMEs are good resources to tap into for new ideas and make sense of seemingly unrelated trends.
The SMEs help teams think about the context, as systems of related elements.
It is common for consulting firms like ours to draw upon SMEs from outside the company, typically from our network of industry and technology experts, for our engagements or deliverables.