How likely could they actually get away with doing this in America?
So theoretically if someone accepted these terms and conditions, broke
them, and Nintendo actually damaged their device as a result and this
went to court how likely would it be that courts would rule this to be
enforceable?
Very likely.
Substantive legal issues
There at least three issues, but none of them obviously prevent this from being valid.
At common law, a consequence determined in advance and agreed to in a contract is void if it replaces easy to determine at the time of breach money damages, or if it is disproportionate to the magnitude of the breach if determining the actually monetary harm for the breach of contract is difficult at the time of breach. Bricking the switch is basically a natural consequences type remedy which is unlikely to be invalidated by a court (particularly since we are talking an item with a value in the hundreds of dollars that could disrupt many other users of the device in multimember online games disrupting the value of what they paid to use). The statutory fine for a single simple copyright violation is a minimum of $750 if it is not innocent (and $200 even if it is innocent), while the device and a few games might be worth $450-$700 new, so it is very unlikely that this would be considered an disproportionate penalty or unconscionable remedy.
The Digital Millennium Copyright Act (DMCA) and the regulations enacted under it overlap with some of the grounds for bricking it, like anti-circumvention. And, courts are not generally going to provide relief to someone who has violated an independent statute through their conduct on some sort of public policy grounds. Put another way, any equitable relief might be denied to the switch owner on the grounds of the Switch owner's unclean hands.
The Computer Fraud and Abuse Act (CFAA) also statutorily prohibits lots of the conduct that provides a basis for bricking the switch. The contractual authorization in the ToS may also insulate Nintendo from CFAA liability for this action, since the CFAA applies only to unauthorized hacking.
Basically everything that is prohibited in (a)-(d) is prohibited by one or both of these two acts of Congress.
There is no requirement that a contractually agreed remedy failed to use a less extreme remedy instead. The analysis only addresses whether the remedy provided for in the contract is grossly disproportionate.
I could imagine some very specific practice, like access for legitimate repair purposes that is recognized by DCMA regulations overriding an otherwise valid ToS term, and the repair shop (or the repair shop's professional or industry association or a friendly non-governmental organization) might have a strategic interest in financing that litigation (although the arbitration forum might undermine this incentive). But, usually, the alleged misconduct involved isn't going to fit in one of those narrow regulatory carve outs.
Of course, for the contractual remedy to be valid, the contract has to be valid. But it isn't obviously unconscionable, and I will make the reasonably safe assumption that there was some sort of shrink-wrap agreement or button on the screen that you had to click agreeing to the terms of service (ToS), before the product could be used (and if there wasn't, anti-circumvention under the DCMA comes into play). The question assumes that the ToS was agreed to and I will as well.
Owner filed litigation remedies
Since bricking the switch is a self-help remedy, the Switch owner, who wants to change that status quo, would have to be the one to go to court seeking relief, and it would usually be cheaper to buy a new Switch than it would be to litigate with a major multinational corporation over its authority to brick your old one.
This kind of litigation could be very expensive. The filing fees alone could exceed the value of the device in some cases. And, if tried in a court rather than in an arbitration forum for some reason, Nintendo would have a decent incentive to appeal an adverse ruling in a trial court because it has a strategic interest in establishing the validity of its policy for future cases (even if it is uneconomic to litigate in this particular case in isolation), while the consumer generally wouldn't have that incentive.
Also, the arbitration clause (linked below) would prevent a consumer win from creating favorable binding precedents for future cases, making the case unattractive for public interest groups trying to support the device owner.
Similarly, the Switch owner could argue in whatever valid forum is specified by the ToS. This document says that the remedy is generally arbitration with a class action waiver, or unless there was a timely opt out within 30 days, which would switch the forum to the courts of Seattle, Washington (King County). If the matter did get into court either from a regulator's lawsuit or a timely opt out, many copyright issues are in the exclusive jurisdictions of the federal district courts.
In court or arbitration, the Switch owner could argue that the Switch owner didn't actually breach the ToS due to factors like mistaken identity, unauthorized use of the device by a thief from whom the device was recovered, or the conduct claimed not lining up with the grounds for doing so (e.g. non-payment of an installment due on an installment purchase of the device). If the Switch owner won, the owner would probably get the cost of having the device and service restored and out of pocket litigation costs. But the question assumes and I will as well that there actually was a breach of the ToS by the owner, which would imply that litigating the issue would be futile.
Regulatory agency action
A state attorney general or the Federal Trade Commission, might have authority to investigate and prosecute violations of consumer protection laws (at the state level, often called a deceptive trade practices act).
But I'm not aware of any consumer protection laws that target this particular practice, and the misuse of the ToS right would have to be very egregious and a gross misreading of the contract that came up frequently for those agencies to take action and for that action to be effective. I'm sure that there could be some fact pattern where some regulatory action might be possible, but I'm not feeling creative enough today to describe one.
In a regulatory action, the regulator bringing suit in court would have to identify and prove that some specific statute in that regulator's jurisdiction was violated, and it isn't at all clear what the regulator could claim in that regard. Simply bricking a device for improperly using it is not generally speaking, prohibited.
