- display a text depending on the price chosen (for registration page)

No, you can only change texts after they've subscribed and only for places that process CBSubs substitutions as it does extend CBSubs substitutions as explained earlier.

- authorize the price changes with conditions (only if the chosen price is more expensive for instance)

No, it's not that complex. Maybe in the future we'll have such an option, but for now we're trying to keep the UI simple enough anyone can configure pricing options quickly and easily.

Too bad in this case we may have to stick with several plans to be more flexible

That's fine. This isn't meant to replace any and every case. It's just a new feature. You either need it, want it, or you don't and that's ok.

No way to condition against the price name with cbif for instance ?

You can but only after purchase and only in specific locations. The substitutions are explained under the Display tab of the Options integration as well as in my blog post below.

www.joomlapolis.com/blog/kyle/18983-cbsubs-options

Or I guess we have to write our own JavaScript which defeats the purpose of the plug-in

If you want to condition text client side then yes you're going to have to write your own JS to do that. CB Conditional may support option selection in the future, but for now it doesn't as this just released.