It's not unrealistic at all, I'm following that exact career path right now. I spent 6 years developing Wordpress and PHP applications and decided last year that I wanted to become a full stack JS engineer.
I found an amazing consulting company who dropped me into React training on day one (having never touched React before). Over the past 7 months since being hired I've built 3 production react apps, am the primary frontend developer for my client's React app and working on a couple internal React/Typescript projects.
Finding the right company that is willing to invest in your career development is crucial. Heck, I brought PHP code to my first JS interview and they still hired me. Most importantly, don't be afraid to answer "I don't know".
Coming from the land of ES5 and jQuery, I found a couple of things to be most difficult when starting out with React:
this** and object inheritance. The key to understanding state management and object properties relies on an in-depth knowledge of scope and inheritance. React employs 1-way binding by default which is extremely important when passing properties to child components.Below are a couple great resources to help guide your learning.