Have they made the switch to something of their own design yet?
Why should they? It's not like the traditional manufacturers do everything in house, I believe most ABS systems come from Bosch for example. (Not a fanboy, mind.)
ABS isn't a core component, even if legally an essential one. Tesla are much more dependent on their battery suppliers (and the performance characteristics of their products) than any auto firm is on their ABS supply chain.
Why should they? It's not like the traditional manufacturers do everything in house, I believe most ABS systems come from Bosch for example. (Not a fanboy, mind.)