It not much time left until Electron be shipping out. How about Shields? Will it be Shield Shield for Electron too? How soon?
As I can see on Electron pinout pinout at Git I still can use my old Shield Shield with Electron. Of course 10 pins will be unconnected but Power, GND, Rx and Tx will be there. Can work until a right Shield Shield is available.
There are no dedicated Particle Electron shields at the moment, but you can use the Photon shields since the devices are pin-compatible (as for the default shield use, some differences in features on the extra pins might be there) - as long the Electron has room to stick out the header (which it usually has on all of the official ones - apart from the InternetButton where you’d have to remove the white cover).
Third party shields need to be checked one by one, but most SparkFun ones look good too.
ControlEverything shields might be different, but they have Electron ones.
One thing to take note of is if the shield needs 5V at Vin, since the Electron - if LiPo powered - will not boost the 3.7V up to 5V on that pin.