I did an RN to MSN in Informatics through Excelsior College and was very happy with my degree program. I'm not sure why you think you'd be "stuck" and unable to work in other disciplines because you specialized in informatics. Most MSN programs have the same core curriculum and then additional courses for whatever you are specializing in. If you decided you really wanted to do NP school and got accepted into a program, you'd already have a master's degree and would just need to take the NP specific courses and do clinicals. The same is true for becoming a nurse educator or clinical nurse specialist.
As far as employment is concerned, it depends on a lot of factors like your background, your experience, the job market, and the type of job you want to do. When I graduated, I had worked as an acute care nurse in ED/ICU for 6 years, but the only informatics experience I had was my Capstone and using an EHR as a nurse. When it came down to it, my knowledge of ED workflows was as much a factor in me getting hired as my degree. Some of my coworkers did get a foot in the door by becoming super users and/or trainers, so if you have the opportunity, it's worth looking into.
Saying that being an NP and being an informatics nurse are different is an understatement. First and foremost, I'd think about whether or not you want to provide direct patient care. If you love being at the bedside and spending time with patients, informatics nursing may not be the career path you want to take. If you like working with end-users, collecting and analyzing data, and designing and building workflows you'll love informatics.