I agree completely. I made a big push to switch from vim to spacemacs so that I could use org-mode for note taking and reduce my dependence on paper notebooks, but the lack of ability to easily sketch really killed it. I'm a geologist so I need to sketch out maps and other kinds of figures that aren't just scatterplots and flowcharts or whatever (which can be done programmatically). If I could have something even quite crude it would be revolutionary, especially if the org clients were improved for iOS with better editing/syncing capabilities and less of a focus on agenda and calendar capabilities (todoist and native calendar apps work better for my job situation, personally). The rest of org is so easy and powerful... I still dream my little dreams but am not willing to learn how to implement something like that myself I guess.

Would this help? https://elpa.gnu.org/packages/sketch-mode.html

AFAIK it supports SVG rendering. Is that not enough or what did you have in mind?