Let us be clear. All that is claimed is access to Satcoms and the passenger WiFi.
No mention of NAV, FMS, FCC or TCAS. Just some vague suggestion that disrupting Satcoms could interfere with FANS. So let's not panic just yet.
As for TCAS? While TCAS can use (potentially spoofable) ADS-B to assist initial target acquisition, the conflict algorithms themselves use only independent range measurement using SSR. To fool it you really would need to hack the main code - it cannot be fooled at a simple data level.