I thought that rendering a font at say 8pt and scaling x2, is not quite the same as rendering a font at 16pt.
I know only one piece of software where it is not the same: TeX changes letter proportions and shape depending on point size, for its built-in CM fonts. But it's an exception. Modern font formats have no provisions for that, and at least letter shapes are never changed (though some software may e.g. change tracking depending on point size).
[Well, to be pedantic, PFB/TTF fonts can be _hinted_, which will affect the way they are rasterized and thus, one might say, change the "shape" of the letters. But this is irrelevant for a vector tool such as Inkscape, and hinting depends on pixels size, not point size, anyway.]
I'm sure that changing the font size will be what most people want, and is the best default, but keeping transforms as transforms should also be possible too.
Sure, it will obey the same "optimize/preserve transforms" switch as everything else. "Optimize" would change font size, "preserve" would not, using the transform= only.