I think it partly depends on what the definition of a 'good coach' is. Is it someone who inspires their students to love skating either as competitors or recreationally, someone who teaches good technique and good sportsmanship and lets medals go hang, someone who creates unique performers, or someone whose students win every medal going? (Of course the platonic ideal of a skating coach does all four, but we're talking about human beings with limitations here). I think all of those can be hard for former champions to achieve because they require going back to the basics and learning a whole new set of skills, the greatest of which is a completely different kind of patience than it takes to be a champion sportsperson. But those who are willing and able to start at the unglamorous, unpublicised end of the pool and do the equivalent of their teacher-training can, I think, make very good coaches indeed.
One thing I have noticed is that good coaches all have what in the education field is called a philosophy of teaching guiding their work, and that's something that one only really develops with time and experience. Mishin has spent decades building his, and we saw what it could achieve in his work with Carolina Kostner last season. Orser is a great example of a former champion who was willing to start at the unglamorous end of coaching and built his skills, his style and philosophy of teaching and his profile from there. Likewise, although he doesn't have as much of a profile yet, Lambiel was learning by teaching low-level students, coaching the Bodenstein siblings when they were still in single digits and doing single jumps, and doing 'polish coaching' along with his choreography work for some years before establishing 3S, and then running the school (including learn-to-skate classes) for a while longer before taking on his first international senior student, and it shows. By starting at the lower levels of coaching he's developed a distinct philosophy of teaching and approach to teaching, that's still in progress but getting some interesting results, and not just at the top - one of his students who's been working away for years at Swiss-cup level just made it into the national junior catch-up cadre in her final year of eligibility and will be able to compete internationally this season and possibly into the future, which seems to be a direct reflection of his approach (that achievements come when a student's mind and body are ready for them and not according to someone else's timetable, so as long as you love what you're doing, keep on working).
Another one I'm interested in as a kind of contrasting case is Plushenko (he makes a good comparison with Lambiel because they're both former World Champions with active careers as show skaters as well as their own skating schools). If I'm remembering correctly, his school teaches learn-to-skate classes as well as competitive skating, and I know he's had some relatively high-profile students. He also seems to be very good at drawing on his experience to work with established skaters who are recovering from injuries. But I don't yet get a sense that as an individual he has, or is developing, a guiding philosophy of teaching or a personalised approach to skills development for his students as yet, and I'm not sure why. It will be interesting to see how how he develops as a coach over the next few years and if a philosophy of teaching does emerge, though. I'm sure it will be quite distinctive if it does, but I'm not sure he's going to be able to create a substantial career as a coach if it doesn't.
I think one of the advantages that former champions have as coaches, though, is that they understand the world of competitive skating from the ground up. They have the ability to not just teach skills, but also scaffold their students through the process of becoming participants in the culture of competitive figure skating, and they have connections that let them network like nobody's business. Getting opportunities for your students is a important part of teaching too!
ETA: Oh, I forgot! (Sorry, this is getting very tl;dr). Aljona Savchenko stepping straight into coaching the Knierims is going to be interesting because it seems like she's skipping over all the developmental stages of teaching skill development. But at the same time she has recent experience of both coaching Bruno in some areas and being coached by him in others as they built their partnership (triple salchows! - and Bruno has a long-standing interest in coaching, too), and her students are adults, not teenagers. Both of those factors could make a difference. I'll be watching closely to see how it goes...
