So basicallly you are not asking to get the old behaviour back, but rather for a visible indication of the mode you are working in.
Do you have a midi controller with programmable lights? A lot of the cheap AKAI stuff can do this, I believe.
Maybe you could solve this with a macro that toggles edit mode and the light status of the external midi controller? I have not used Nuendo for a while and do not know if a combination of generic control and the macro engine can be used to get this done, but if you are on mac I am quite sure that this could be solved with keyboard maestro that can automate midi and keystrokes.
I personally think that it is wonderful that this has finally been adressed, I asked for it since version 3. (but have since switched to PTHD where it has always been working as expected). I really think that Steinberg is doing the right thing here, to start to sort the small things out. I also noticed the new smart tool that is another step in the right direction.