I have been obsessing over gearing for a new build, and I though I would post up my visual aid: a plot a gear inches on a log scale, for various drivetrain configurations (all points are for 26 inch wheels). Ideally the points would be equally spaced on this scale.
The first set of points, the blue triangles is the gearing for a 12-32 8 speed cassette with 22T/32T chainrings, which I used for many years.
The second set of points is the standard 11-36 10 speed cassette with 24T/32T chainrings up front, which I have been using more recently.
The next set of points, the red circles, is the SRAM 11-speed configuration with three different chainring sizes.
The purple triangles are the 10 speed 1x conversions: a 10 speed 11-36 cassette with the 17T cog removed and a 42T cog added, again plotted with three chainring sizes.
The green circles are for a Canfield micro-drive hub with the Canfield 9-11-13-16 cogs mated to the bottom end of a 10-speed 11-36 cassette.
The x's are for a Canfield micro-drive as above but with a 42T cog added and the 21T cog removed. Not sure how easy that would be to do, as the cassette would have to be drilled to separate the cogs. I think I saw someone saying they had done this on MTBR.
The final row is a Leonardi 10-speed 9-42 cassette for a SRAM HD style freehub. I don't know if or when that cassette will be available.