Well, actually, linguists view language as non-linear and, morever, descibe language by using non-linear models and mathematical notations and illustrate them using graphic software. :D We've come a long way babe.I think it's not unconventional, only thing being that grammarians (that's just speaking broadly and jokingly) fear treading on unfamiliar territory that is the domain of mathematicians (or graphic artists!!), such as graphical representation of an idea.
In terms of a linear explanation, I agree whole heartedly with you on that point. Describing Tense in terms of a lineal model, a line, is unconventional, and hence my noted advanced apology.I had thought of using the horizontal line (great minds think alike) to pictorise the explanation of tenses, but I have decided very decidedly not to, because experts will look on it not just with disdain but total consternation!! And my poor text will be still-born, looking more like a book on geometry!!!