I don't have a solid answer, but I would argue that it can eventually potentially be a career killer.

Here's my argument: a good chunk, perhaps the majority, of the business is now cloud-based. Being stuck in a non-cloud-based environment can potentially put you out of touch with the prevailing and constantly-advancing tech stacks that the rest of the industry is using. You'll likely be working on a different set of problems, limitations, solutions, etc. than what the cloud-industry deals with. And as such, it could put you in a Plato's cave type of situation, and when it's time for your next job hunt, you'll be severely disadvantaged.

Example: let's say you're a mainframe engineer at IBM. You'll make a shit ton of money, sure. You have a nice fancy name on your resume, absolutely. And the experience is probably priceless.

But it's also worthless to other jobs, if/when you start job hunting. I mean, great, you were a mainframe engineer. You have an engineer's set of skills, absolutely. But you lack industry experience, and you'll have to find an employer who is okay with letting you catch up on the job. Most expect some level of catching up, but not from no experience. You've successfully tunneled yourself into an area of the industry.