It seems to me that it must be possible to judge spoke tension by ear, rather than tensiometer
When you spin a wheel and let an allen wrench or screwdriver blade lightly tap/bounce off of the spokes as they go by, each spoke will resonate with a pitch that is completely determined by its tension (and thickness and length, but those will all be the same for the same wheel). Left side rear spokes will have lower tension/pitch then right side, but it's easy enough to just strike just rights or just lefts.
For a wheel just built from a perfectly true rim (so no spoke has to work extra hard to pull the rim true in a certain spot), equal tension should mean every left-rear spoke rings the same pitch, every right-rear spoke rings the same pitch, and every front spoke (assuming non-dished) rings the same pitch. It seems like instead of a TM-1 and a deflection-force conversion chart, it should be possible to use a tuning fork and a pitch-force conversion chart.
And somebody (maybe even me) should be able to convert the statement "A wheel with spokes that are within plus or minus 20% of the wheel's average spoke tension is generally considered to have acceptable relative tension." into "A wheel with spokes that ring with pitches within plus or minus X...", for X=minor third, or something like that (2x pitch = 1 octave, but does 2x tension = 2x pitch?)
On a related note, would anybody start a wheel truing (building?) by first setting all spokes (per side) to equal tension (pitch) according to rim spec (say, hypothetically, Mavic Open Sport rear takes A440 on the drive side and E-flat below that NDS), and then removing any residual runout and hop?