The I6 in my truck will throw flames out of the collector of it's exhaust manifold. Your point?
ALL gasoline burning engines spit fire. ALL of them. Yours, mine, the weedwhacker the neighbor annoys you with at four in the morning, all of them. Two or four stroke, piston or wankel, it does not matter, they all spit flame out the exhaust port. The fuel-air mix just doesn't have enough time to burn completely before the exhaust valve opens if you've got any significant amount of throttle or RPM on.
Only if you're building a race engine. If you're building a street engine you do not need to wrap the headers, even on a wankel. Yes, it will get hotter than it would on a piston engine, but it's still not going to get hot enough to warrant wrapping it.
That's pretty standard for every car ever made. The factory manifolds are designed for packaging and noise reduction, so they end up quite restrictive. My engine stands to get the same boost when I install a header.