I would say, it’s definitely possible!
I’ve been a multi platform developer for around 6 years now. It is very simple to get a working knowledge of both platforms as they’re actually much more similar that people say they are.
The hardest part is keeping up with the changes on both platforms but with time and effort you can get around this. Likewise, you could be an expert on both platforms for sure, but that depends on how easy you learn and how invested you are in your learning – you’ll be as good as the effort you put in.
Being a complete expert in both platforms is realistically going to be near impossible, but also being an complete expert is one platform is basically impossible like @ignazioc mentioned. I tend to focus on things that are the same between platforms to ensure that I can act as a bridge between projects on both platforms.
Personally, I think it’s incredibly rewarding to be proficient on both platforms, and it has opened up huge opportunities in my job to be so. I can have conversations with either platform about specifics and lend a hand to any project that goes on.
I say, you should definitely give it a go and report back how you find it