Will Silabs offer a SIGFOX stack for EFR? I saw some presentations from Sigfox with Silabs radios but never heard about a SIGFOX product.
Silicon Labs is not currently offering Sigfox enablement on EFR32 products. However, there have been several customers who have managed to successfully implement a Sigfox solution on EFR32 by working separately with various 3rd party engineering houses.
There are also several module manufactures who are using EZRadio Pro devices to implement a complete Sigfox solution.
These are available through Avnet-Silica: https://www.avnet.com/wps/portal/silica/products/product-highlights/2016/td-next-rf-modules-for-iot/