The SX127x family of chips from Semtech are modems supporting both LoRa and (G)FSK modulations (including ultra-narrow band FSK). Coupled with a microcontroller implementing the relevant stack(s), they are already used for with following IoT network protocols: LoRaWAN , Sigfox , Wireless M-Bus , DASH7 and Symphony Link. They could probably also be used with EnOcean, Zigbee sub-gigahertz and Z-Wave but I know no examples of that, and some of those are very closed ecosystems.
LoRaWAN stacks are available publicly, license-free. The availability of other stacks is variable, and you will have to do the co-integration of several stacks yourself. If you only need to support one stack at a time, and just want the ability to switch networks by re-flashing your micro, then the problem is simpler. With a modem from TI or SiLabs you can support most of the FSK-based protocols. With a circuit from Semtech you gain additional support for the few LoRa-based protocols.
To future-proof a LPWAN product, some modules are already available with a dual LoRaWAN/Sigfox stack: http://www.nemeus.fr/en/nemeus-mm002-2/ You cannot connect a module that is not qualified by Sigfox to the Sigfox network, so using this kind of module can save a lot of time and hassle.
If a module is too big, there is a SIP combining a SX1276 and a microcontroller: http://www.acsip.com.tw/index.php?action=products-detail&fid1=19&fid2=&fid3=&id=79 but in that case you will have to provide the stack yourself.
There are no single chip available right now that combine a microcontroller, a LoRa/FSK modem and a ROMed stack like you can find for Bluetooth. Given the minimum size requirement for an acceptable 868 MHz antenna (> 10 cm²), gaining a few square millimeter of chip area by doing a RF SoC is probably not worth it.