According to this thread, specifically post #21:
"That's exactly what we were told: those 8 1Ms (4 white, 4 orange, the ones I saw had 5–10k miles) will be unloaded on the used market (somewhere...) within the next few months after they replace them imminently with M6s.
Glad they didn't swap them out sooner — the M6 would have been far too big for that fun little autocross track."
http://f10.m5post.com/forums/showthread.php?t=758073
So for those looking, stay on high alert (not sure how they will be placed, my guess it would be through Manheim or similar, which is not open to public)
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2011 BMW E82 1///M: AW, all options; Renntech, Akrapovic, Forge, P3, RevoZ CF bits, many mods
1988 BMW E30 M3: Hennarot, S14, stock
2018 Porsche 991.2 GT3: PtS, CXX, LWBS, PCCB
1998 Porsche 993 C4S: Zenith Blue, last aircooled widebody, Bilstein PSS10, Fister II + Fabspeed exhaust
2008 Audi B7 RS 4: Sprint Blue, Audi Exclusive Euro Bucket Interior, Premium+Titanium, many mods