It's interesting to me that the main people who talk about using hybrid approaches to Agile are traditionally trained project managers. They believe there is a special blend of waterfall and agile techniques that will yield better results than either approach alone. They want to take the best of both worlds. I think they are misguided.
What ends up happening is that these project managers take their traditional project planning and execution approaches and then they add bits and pieces from Scrum or other agile approaches. They begin to call their existing waterfall phases "sprints" and their requirements "user stories". They have a meeting that they call the daily standup meeting, but it sounds more like the project manager is conducting an interview of each team member. And occasionally they toss out some phrases they've heard like "fail fast". They even go so far as to call themselves Scrum Masters.
Changing the name of something doesn't change what it is. I can call myself a world class athlete but that doesn't make me one. In the US we have a Secretary of Defense but that doesn't change the fact that offense and war is their main focus.
The idea of a hybrid approach between traditional PM and Scrum falls somewhere between wishful thinking and outright crazy. How can you reconcile the project manager as the "single throat to choke" in traditional approaches with the self-organizing teams of Scrum and Agile? How do you reconcile sustainable pace and team commitments of Agile and Scrum with the fixed dates and scope of traditional approaches? It simply doesn't work because we are talking about two fundamentally different and oppositional mindsets about people and teamwork.
The people advocating for hybrid approaches don't really understand. (BTW, I hate the expressions "Scrumerfall" and "Wagile"!) ) Last week I met with a traditional project manager who was being tasked with leading multiple Agile teams. We talked for about an hour and in conclusion, he asked me for some templates he could use. That was all he felt he needed. So he has zero experience with agile, he is taking on a large agile program, and all he needs is a couple of templates? Maybe he slept at a Holiday Inn Express?
It doesn't work that way with Scrum. Scrum is a framework for organizing teams and building solutions based on Agile Values and Principles. I don't recommend tailoring Scrum even in organizations that are transitioning completely to Agile. It's not helpful to pick and choose the parts of it that you like or understand and want to implement.
What's behind the desire to mix methodologies? It seems like a lack of true understanding, as well as fear and resistance to change. There is a reluctance to let go of what has worked in the past. And an even bigger reluctance to let go of control. And in the case of the templates project manager, it's a belief that anything can be managed with the right template.
I am not saying that traditional PM methods aren't successful. I just don't think they have a place on a Scrum or agile team, especially if you want to call what you are doing Agile. Stop mixing things up and use the right approach for the goals and culture of the organization.