Baseline Grid
observablehq.com
observablehq.com
Except it does, because (as you say) it can be done using current layout technology - what you call "fudging with margin and padding" is what I would call "using margin and padding". No doubt a design app to help work out those values, or some computation using CSS's calc(), or even some progressive enhancement using JS, would be helpful if the design calls for it but designers and developers desire to avoid those using what's there now should not be what drives web standards. "This is not possible with current tech" or "The current tech is inefficient and bad for perf" is what should drive standards, not "I don't like the current tech".
Also, as a bit of a side note, the draft spec you linked to includes the following line: "And careful calculations can be thrown off by user stylesheets." The author believes a layout being altered by the user's browser choices is a bad thing. I disagree with that so much. Giving the user the power to completely change their experience of a site is one of the best things browsers do.
https://chrome.google.com/webstore/detail/grids-by-color-set...