It depends on what your career objectives are. If you intend to found a start-up you can of course choose your technology stack and ignore Xamarin completely if

It depends on what your career objectives are. If you intend to found a start-up you can of course choose your technology stack and ignore Xamarin completely if you wish. However if Xamarin takes off in the way I hope it will and becomes a high-quality product under the auspices of Microsoft, I believe it will become a vital skill in the marketplace. And then, it would be like not knowing React or Angular as a web app engineer. Depending on the company's technology choices, that might not matter, or it might mean you don't get the job.