I was just thinking that. o_0 I was imagening a world where people use roman numerals while writing numbers down and doing simple calculations while using arabic numerals in maths and such. This would need a really small educated class, of course.
Would it be possible to have both the Roman and the Hindu-Arabic systems exist side-by-side for different purposes, as was the case with the Chinese numeric systems?
even writing large numbers and decimals isn't much of a problem compared to what doing calculus, trig, or analysis with them would be.
We're sort of there now, in OTL, although our purposes for Roman numerals are inscribed in very small spaces (clocks, years on monuments and in movie credits, outlines, counting kings and queens)
OTOH, it is possible that we might use the Arabic/Indian system of counting but substitute the Roman numerals in their place, for some reason. That would probably require the numerals being compressed into distinctive single numbers, e.g. VIII would become a V with three vertical lines through it, so "VIII" would be unambiguously "5,111".