I wonder, what are some real or potential and purely theoretic difficulties you may face if you decided to implement the split-complex unity $j$ such that $j^2=1$ along with already existing complex unity $i$, with similarly extensive rule-set?
I mean, implementing $j$ immediately adds support for split-complex numbers and tessarines (which are isomorphic to all bicomplex numbers variants).
One would be able to write a tessarine as $(a+bi)+(c+di)j$ or $(a+bj)+(c+dj)i$, the both being standard forms.
On the surface, implementation seems not to be difficult as tessarines are both commutative and associative, which would allow to keep the usual rewriting rules.
Yet, they have non-zero elements by which one cannot divide. This may bring some difficulties. But since there is already zero, by which dividing is impossible, maybe this is possible to overcome.
Maybe some additional infinity-like symbols would be needed (but maybe not).
Maybe Solve and Reduce would need to produce more solutions.
What the developers say?
A separate but related question: would implementing dual numbers unity $\varepsilon$ be easier or more difficult?