We can make those limits be any two positive numbers that add to $1$, or we can make them nonconvergent. The reason is that in any interval, we can construct $A$ and $B$ on that interval by using the iterated fat-Cantor set construction (as described here), and we can make $A$ have arbitrarily small measure on that one interval, which is what bof refers to in his comment. Now, by
By repeating those small-measure sets on successive intervals, or by using large-measure sets as desired on successive intervals, we can control the asymptotic measure as in your limit value of your asyptotic measure so as to realize any desired value or a nonconvergent value.