Hello! First and foremost, I'm new to the forums so apologies if this has already been suggested, I didn't quite see it at a first glance. I'm also not currently aware of this being a feature, but if it is, fantastic!
I would like to suggest the ability to set the stroke width of an object to a variable, rather than inputting the actual width. This would make it a lot easier to adjust the line width on MANY objects if you're working on a project where you may not know what to set the line width at, or if you unknowingly used a line width too small. The variables could even hold other types of data, like color, opacity, etc. There could be a variables panel where you can add a variable, select what kind it is, and input the current value of the variable. Maybe it could even be based upon other variables if you always wanted to make sure VarA was always twice as big as VarB, in terms of sizing.
If something doesn't quite make sense, feel free to ask questions as sometimes I can miss details. Thank you for taking your time to read this!