Initially I tried this with my large setting on my Keurig and it was too watery. I suggest 8oz water or less.
I'd like the final drink to be a bit darker. I may try the Splenda brown sugar.. or maybe a darker rum.
The nutmeg/cinnamon does not dissolved in the water so the last dreg is a bit chewy. Less nutmeg/cinnamon and more frequent stirring may help this. Otherwise just plan to dash (or chew) the last sip.
Swerve is an alcohol sweetener. It has the side effect that everything you eat/drink after the Swerve will taste a bit sweet. I suppose you could substitute other sweeteners. MMV.
The rum and the sugar potentially make this not "keto". If you leave out the rum and use a sugarfree sweetener than I suppose this is like a Bulletproof coffee minus the coffee.