It looks like @martijnr mentioned WKT in the original discussion regarding the format of geo data collected by ODK clients here. I'm not entirely clear from reading the discussion why it wasn't considered, does anyone remember?
I can also see that @Rijvi_Rajib wanted to use WKT in this post.
In principle, producing WKT (or another standard format used by GIS tools) seems like a really good idea. In practice, what would that take? Adding an attribute to the existing geo controls? Adding alternate geo controls? It would probably be important to keep supporting the existing format for continued compatibility.
@mathieubossaert do you have a sense of how you would like to request WKT output when building a form?