What codec am I using?

In FCP7 you used to be able to select your editing codec and change in manually whenever you like. If there was footage in your timeline, it would un-render and you'd have to re-render it.

In Resolve it all depends what clip you open first, then you have to remember the codec settings of that clip and you can't change it at all after that first import.

Do you think Resolve is missing this feature? Or do you think it's a step forward not having to worry about codecs anymore?

There is no "editing codec" in Resolve. You can optimize or cache your footage to other formats if your computer can't handle your footage.

Definitely a step forward. Having to transcode everything to ProRes in FCP or DNx in Avid is a limitation of those programs. The footage agnosticity of NLEs like Premiere Pro and Resolve is the preferable design.

Though I do think Premiere Pro takes this one step farther, attaching the Timeline Settings to individual timelines, rather than a project-wide setting.