Hi Gary,
Your work with quaternions is fascinating. You begin by noting that time is viewed as either a scalar or a vector ("dimension"), and choose scalar, with complex 'i' viewed as a dimension.
Since we have discussed Geometric Algebra, I thought you might be interested to know that a recent book Understanding Geometric Algebra for Electromagnetic Theory, by John W Arthur, treats time both ways. He first develops Maxwell's equations viewing time as a scalar. After this he treats time as a vector and shows how this leads far more naturally to the fully relativistic formulation compatible with Hestenes 'Space-Time Algebra'. In neither of these is the complex 'i' a vector.
What's so special about geometric algebra is that every term has both a geometric and an algebraic definition, unlike every other branch of mathematics. In this scheme it's probably more correct to say that the complex 'i' does not appear in GA, since, although it has the algebraic value of the square root of -1, it is a pseudo-scalar, which is a different beast. Even so,in 2D it reproduces the complex plane very nicely.
I think of the 'i' in GA as an operator, and specifically an analog of the Hodge duality operator of differential geometry. It has the effect, when operating on a term, of transforming the product into the dual of the term being operated on. This is quite different from the scalar 'i'.
I don't know if this is any help at all, but I find viewing 'i' as the operator in GA to be quite helpful to my own understanding. I don't know that it applies to your immediate work, but since GA includes quaternions, and since you seem to be moving in the direction of GA, I thought I'd put my two cents in.
And thanks for your comments on my paper.
Best regards,
Edwin Eugene Klingman