Rather not, you would have to transfer the viewfinder live picture and the final image over i2c, which is way too slow i guess. OTOH, Pentax was recently announcing a wifi sd card for the K3 which supports tethering including liveview over wifi, so in principle just make an TOH adapter for the K3, write an app and you are there Would not match my definition of "pocketable" though.

A bit more serious: the Sony DSC-QX100 and QX10 are cam "modules" for mobiles attached only via wifi, something like this could be possible for the jolla, too. But they are quite bulky.