MIFA Antenna Design for BLE in KiCad?
There are two ways to go about this, none are pretty.


MIFA antenna shape can be broken down into simple rectangles, in the footprint editor, you can add pads of the required size and calculate its position, you will need to calculate lot of offsets as the pad location is referenced to its center and I assume the MIFA antenna shape will have dimensions between edges.
Using inkscape. Create a shape in inkscape and export it to png. convert it to binary image using GIMP or similar tools, next use Bitmap2Component, open image file by clicking on Load bitmap set the resolution so the image is not scaled. Set the "Format" to Pbcnew(.kicad_mod) and "Board layer" to Front silk screen. Hit export.
This will generate component file with silkscreen of the custom shape. Now open the component file in a text editor and replace F.Silk with F.Cu.
Now open this file in footprint editor and check if the custom shape is on F.Cu Layer. Now add a pad and place it inside the custom shape, nearest to where the wire would connect. Save it and that is it.
(I recommend starting with a square shape and then start with the antenna design after you have got the process).


Sadly, there is no other way around it as far as i know.