The ease of adding electric/kick start is model specific.
Electric or kick starting can be added to any 5 speed bmw airhead .. reasonably easy .. just a question of money and time.
Adding kick start to most eclectic start only bikes is for most probably cost prohibitive. And they can be bump started on reasonable surfaces. But I carry jumper leads ... probably weighs less than a kick starter system anyway
Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S