What are the necessary prerequisites to offer, launch, and embed learning processes sustainably nowadays?

Philippe Seynaeve: Each word in your question counts. 
With respect to "launching and embedding learning", both the "prerequisites" and the "sustainability discussions", are, in my view, concepts that are still overlooked and have yet to be inked. They are valuable anchoring points that need to be relied upon when genuinely working on reorienting or innovating learning practices in a company.  
I will argue in favor of investing more time in exactly these parts of the "iceberg", so to speak, rather than just the tip. 
If we want to operate in a more sustainable way in the field of learning, we need to question the current and envisioned models, as they are tied up with organizational cultures. We also need to use specific, actual figures about the outcomes of HR-/-training administrations, and so on.
It may be hard to admit, but HRM policies in both public and public organizations often result in bureaucratic practices and concerns - and are kept alive as such, regardless of the indicator on the waste-o-meter - and regardless of whether we have baby boomers, gen X, Y, or Z on board or at the helm.
In my view, quite often - and unfortunately - training and learning initiatives are conceived of as mere fireworks.

What are the roles of edtech, change management, project management, learning culture, user motivation, etc., in this effort?

Philippe Seynaeve: If I understand your question correctly, you begin by referring to IT solutions in our field and also to the related, general work methodologies. In my experience, these have been at hand for ages now and, considered as such, work very well as levers when handled skillfully. 
In comparison to other domains, the "entry points" for agile, creative, structural change management surprisingly remain relatively scarce, given the foil of social and technological shifts.  
Why is this? Silo-structures and mentalities? Management and middle management's red tape? Lack of concern for what people - and not "resources/users," - actually, experience, etc.? 
Could it be that an overall product logic, literally and figuratively, is predominant? I would strongly argue that we need to place process - for lack of a better notion - over product.

How would you picture a perfect learning scenario in the future?

Philippe Seynaeve: Let's say that I am not really taken by the principle of the "perfect" something - be it a scenario, solution, approach, or product. 
Though I know this an old-fashioned constructivist approach, I think we could proceed by delivering "building blocks" that are thought through and timely, with strong involvement by both people from operations and innovations - wherever they are.
Should I wander on the "perfecting the learning scenario" path, I wonder whether there are additional or alternative "monocles" to look at organizational learning, people development, etc., rather than the current ones that all parties involved hold on to so tightly. Can the matter at heart here be viewed, be approached, for certain aspects, for instance, across organizational boundaries - which are in place in ways that are so firm, costly, and wasteful? Are the "resources" that are at the heart of the matter here not a scarcity and thus quite precious or valuable for the corporation and, of course, and foremost, for the individual? Aren’t they a scarcity to cultivate today more than ever?