Console and phone manufacturers have chased this dream for decades and each and every one has been hacked to run arbitrary code and applications that are supposed to ‘only run on trusted hardware’.
You can make it difficult but defeating an attacker who can touch the hardware is for all intents and purposes impossible.
edit I found that Microsoft did the smart thing like Sony did with the original PS3 and allowed people to run their own code (but not XBox games) on their consoles, removing a large incentive for people hacking the console.
That doesn’t automatically make the security watertight though.
"Never" is a strong word, but given that they're already previous generation devices and haven't been properly compromised yet, it wouldn't surprise me.
You can make it difficult but defeating an attacker who can touch the hardware is for all intents and purposes impossible.