So short answers to some of your questions
1. I have assisted with a previous kit build just not a vans product,
2. I have no intention of exceeding Vne, however the reason for the flutter analysis info is to correlate it with increased performance of a different power plant choice affecting Vne Limits especially at higher altitudes.
3. Life insurance is paid up however I have no intention of getting myself in that kind of trouble hence the questions for feasibility and the most likely outcome of building a stock 12is,
4. My interests are in hanging a 15is of the nose so while I do anticipate some weight/cg considerations its not crazy out of the ball park to imagine that a different engine in the same family is possible.
That being said the biggest concerns would be flutter at altitude with the greater performance of the engine, and structural design limitations.
Overall the biggest limitations I see with the 12 is the fuel capacity, of course everything in engineering is a compromise so addressing that faults as far as my mission parameters go has secondary impacts that can potentially be addressed with the other power plant options already available from Rotax.
FWIW, I am an Engineer in aerospace, and was just looking to do feasibility analysis if the data was available, I am pretty sure the CG limits I can find from the weight and balance sheets then I can just do calculations with my intended changes.
But really my larger concerns would be structural load/design limits given the additional fuel and engine weight, and flutter analysis at altitude given the improved engine performance.
Then again who knows what vans has down the line with the upcoming Proposed LSA changes, it would be really nice if they ever got the IMC change through although I don't know if they are really pushing that.