Please get back to me once you've gotten a multinational corporation to agree to this (or any other candidate-provided clause) for a non-executive employee.
The issue is that in many countries, employees don’t actually have contracts. Lawyers will go to great lengths to ensure that offer letters are not structured as contracts. It’s important to keep the distinction in mind.
I find it odd that people are fine with contract negotiation when it comes to remuneration but treat actual contract clauses like holy text that can't be changed.
There's even a good chance that what you think is "unchanging boilerplate" is boilerplate that gets updated all the time and barely anyone is on the same contract anyway, or that it is very job role or department specific.
That said, I've mostly worked at SMEs which can be more flexible anyway, and getting a contract change is a good indicator of their general flexibility so perhaps works as a good filter too.
Last time I requested a change in the contract it took them almost one month to approve.
So if they need to hire someone asap, then it may not work, but on the other hand that is a red flag.
It's of course easier in smaller companies, where there is not many people in the chain that need to look over the paperwork.
I think many people fear that if they start "making problems" they won't get hired, because next candidate may not be too fussy. But I think that is a wrong way to look at it. If you don't stand for yourself, you are unlikely going to stand for other things, seemingly less important and employer may see this as a bad trait. Like imagine a task is being proposed and from your own experience you know it is not going to work, but everyone agrees it should be done. You could keep quiet and hope you'll not be the one to do it or you can start "making problems". Which worker would be more preferred?
I don't think there are many situations in which an employer is positive about a non-executive employee rejecting their contract offer and proposing an alternative with fancy legalese clause awarding themselves a [$amount] bonus up front in a manner which creates the most complications for the company's lawyers and auditors. It's certainly something (and someone) very easy to say no to.
That said, the relocation packages I’ve seen have been effectively similar to this. Having the offer revoked for cause (e.g. you lied) might cancel it, but getting laid off wouldn’t. Obviously not true everywhere though.