Plasma is dead: https://www.coindesk.com/as-plasma-stalls-snarks-become-new-hope-for-scaling-ethereum
Plasma isn’t dead: https://blockchainatberkeley.blog/plasma-isnt-dead-7d0b8c16ad2e
Plasma is very real and very much still actively under development, despite a few iterations live in wild, ex. Loom Network, Bankex implementations of Plasma Cash. One need only look at ethresear.ch and filter on the Plasma tag to see as much.
Additional implementations in R&D including: