Well , not for earth based life as we know it , anyway.
M stars have so long time spans in the main sequence that any possible path to life we could conceive has had at least one chance to arise and prosper.
I think that the main problem with habitability in the M dwarfs vincinity are they tendency to flare. Of course , maybe life in those systems need the flares as trigger for their life-cycles. As always , we are limited for the one sample we know of habitability conditions.
I've skimmed over the paper , and seems to be very sound , albeit there are factors i don't see there , like the ratio of fisionable material , thickness of the crust and mantle , etc , to better isolate the factors that could lead to the outgassing being an important factor or a minor player. A big magnetosphere , proportional to the one on Earth might made a huge diference on the results.
As far as i can see , they had only considered the core as a conduction mechanism for heat transfer on tidally locked planets, wich is a safe bet on the planets around the hz of a M star on the long run, but not a sure thing. Molten cores and liquid mantles could make the tidal lock a little slippery to reach.
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