[megameter]

I think this is more a case of the laptop being the 21st century guitar, than any instrument being "obsoleted". The trends in popular music have followed a min-maxing of physical logistics, loudness of sound, and timbral flexibility relative to the era and setting:

The railroad preceded the rise of the large, Sousa-style marching band, which also made use of the loudest instruments of the era(brass). After electric amplication set in you got an era of radio crooners and smaller-piece popular groups, which ultimately gravitated towards the now familar guitar-keys-drums arrangements by midcentury as the nascent rock band could fit that gear on a bus and get a wide timbral variety with use of amplification and effects without relearning the instruments. The guitar in particular has a good ergonomic profile while also being amenable to amplification and effects, hence the stereotype of the "travelling guitarist" coincides with its central role in large arena rock productions where a three or four-piece plays to an audience of tens or hundreds of thousands.

The laptop fits in with the trend by being even smaller, more portable, more flexible. It fills in nearly every need for back-up, so a solo act can sound as big as desired. And it can be used in its own right as a performance instrument, though computer keyboards aren't tremendously expressive interfaces in the way guitar strings are. (For that, there is always someone selling some kind of new controller interface idea. Though they have a habit of not sticking...)