Here is a simple script to create a variable pitch helix, at the origin.
It is based upon mathematics here:
https://www.zwsoft.com/support/zw3d-base-skills/1378
(Updated corrected link Nov 2023)
I did a pdf with additional information and algebra.

Note: For non-variable-radius helix, use the regular MoI Helix command.

Note that some protection from division by zero is included, which could possibly occur due to length of zero, or some negative pitches.
A better programmer might have used catch(e)?
Some negative entries produce different shapes, or no shape at all.
Based upon limited testing, the program does not hang up MoI.

I spent a lot of time trying to graft it onto MoI's helix script, which is fairly complicated, by switching it to an interpcurve, but
finally decided that the user could do a cplane if desired.

- Brian