Am I naive to think I can focus on professional programming and still be active in the field of CS as a whole?

I am a professional programmer with a PhD.

I have had a colleague, who was working as a programmer and continued even publishing in his unrelated field (chemical engineering/textiles), so if you are dedicated, it is even easier for you to do, since your area might be related, but still it is not a light undertaking. But if you can find a more research heavy R&D position in the industry, of course that would make it easier.

I am personally planning to teach adjunct classes, to keep me fresh about theoretical basis.

Hope my two cents helps.

I was discussing your question with a software developer and here is what came out:

Software development require some specific skills you will develop in the job, and you will surely not be able to be an expert in development as well as, algorithmic, cryptography, network, AI etc... But if you want to keep working on some other computer science subject, it depends where and which project you decide to work as software developer.

If you develop an authentication server or an anti-virus you will still have to keep up in computer security, if you develop a network layer for a game you will have to know about how a network work etc... of course you should probably avoid to go to a company that design web sites or implement yet another client data base...

And as always: what ever you are interested in you can continue to be interested outside of your work.