So, I could not find alternator issues on the 900rr fireblades.
However I burnt one up.
This information might very well be interesting to others too.

So the story began about two years ago when I went into Amsterdam city centre. Traffic was slow and everything was hot.
After about 20 minutes the bike ran so hot the fan went on and since the rpm's were low my battery drained.
When I wanted to ride again after smoking a nice cigar in a lounge (you know what people might think when I mention Amsterdam) the bike was cooled down I ran the bike on and went home without issues.
After this the bike always had some difficulty to keep the battery charged and start ready.
I was suspecting the voltage regulator since this is a common issue but at 4k rpm it still made 13V.
As an experiment I bought a voltage regulator from Aliexpress for $25,- and tried again.
Then the bike made 13,2V at 4k rpm.
Also the bike had a lot less problems keeping the battery charged.
Still I did not trust the issue especially since the alternator should be able to provide 465W!

When I measured the three wires coming out of the alternator I measured 8,4VAC/ 9,2VAC/11,0VAC
This was the moment I suspected the alternator. And when measuring the alternator wires resistance to ground it measured about 6 Ohms. But when connecting a powersupply it made a short (3,2V at 5A)
I opened up the cover and directly got my answer.
The alternator burned up at one point.
When searching for second hand parts I saw that all the alternators for sale had the same patern in discoloration.
Light brown on the low side and dark brown on the high side.
This means that a lot of these alternators should have similar problems, but I never had real problems although it is toast.
The internet said this is a very common problem due to the fact that the wiring is on the thin side for the power and environment it has to function in.
They sold a stator that costs $/€159,- and has thicker wiring and could increase power with about 15% and reduce heat because of the lower resistance.

All this results in 3 questions:
- What will the voltage regulator think of the increased power?
- Does anyone else have had similar problems?
- I'm an automotive engineer and I could think of quite some other improvements for this alternator, but has anyone else messed around with this? I don't need to re-invent the wheel so to speak

Burned up alternator