[Dev-luatex] Math sizes & styles

Can a math layout like the one of the attached image be obtained with TeX? I think it is impossible. The size of the fractions is slightly smaller than that of the main text, and the script sizes for both of them are the same. When is it planned to make configurable the hardwired set of math styles as well as the tree of math style changes, if planned at all? In this example the changes from the main style to fractions and scripts would need to be decoupled. Happy Christmas Javier A. Múgica