I see MWStake as a collaborative effort by consultants, and their customers. Those are the people with a stake. I suppose you could include individual users of MediaWiki software (I setup a wiki that I use to jot down my memoirs and gardening tips, and recipes) if those users collectively feel that they don't have adequate voice in the MediaWiki community. But let's look first at the businesses who's product or service depends on MediaWiki software.
Some companies literally have MediaWiki at the heart of their business technology platform. They have a business need for content that must be indexed, easily edited, or classified etc. and have chosen to use MediaWiki over custom software or off-the-shelf CMS etc.
Some companies use MediaWiki as part of their tech stack, in a 'traditional' role: usually for documentation (especially for software documentation - but it could be for any process documentation or general documentation) and knowledge sharing. These companies have chosen MediaWiki over competing documentation or knowledge platforms because of it's flexibility, familiarity, ease of use and the ability to 'control' and own your content.
Regardless of the type of company, and their use of MediaWiki, they are a stakeholder in the development and feature set of the platform. They need to know what's coming, and plan accordingly. They need long-term support.
The consultants who offer MediaWiki upgrades, installations, training, support, hosting and other services are obvious stakeholders in the software.
I think these constituents need a way to communicate with each other. A way to find each other.