Webflow is the ultimate tool for me, and it just keeps getting better. I'm bored of hand coding HTML & CSS.
The best thing, is that you can override whatever you want right from Webflow's interface.
I was disappointed that the grid system does not support RTL, but was astonished by the simplicity of the quick workaround.
In your website design mode:
Highlight body tag.
From the style panel, go to Typography, and toggle "advanced".
Click the little square button that says "RTL".
In your website custom HEAD:
float: right !important;
Save, and publish.
If you want your website to display the columns in RTL in design mode, it won't be default... it's a know limitation.
However, if you like to hack more, check my other post in here.