An option to normalize the rendered .wav with a headroom of N dB would be great, and even greater would be a checkbox to adjust the master gain accordingly…
Sorry, i disagree because:
why not do the normalising in the song before rendering?
Renoise has an excellent feature to detect clipping, and is packed with compressors and such.
Maybe a compressor on the mastertrack saves your day? 
Of course, feel free to search a vst or something that does
the normalizing for you on the mastertrack.
I only can think of a compressor effect, unless you find something better 
The softclipping option is one of the options that you can use as a solution for this problem. (highlight the mast track and then select the master-track options in the DSP rack)
And if one uses the compressor on the final track in combination with vV’s tip, you’ll note that there is still no clipping harm done 
Great program, we love it.
Because rendering is often much faster.
Normalizing and compressing/limiting are two totally different things though…
I wouldn’t consider this a priority.
Everyone probably has external tools that they use for things like this already, unless they’re going the already suggested way of compressing/limiting (which of course is not the same thing as Johann correctly notes, but I can imagine how some people would actually prefer it!).
You could even load your rendered track as a sample, hit “maximize” in the sample editor and then save it again 
But… if the to-do list is getting short… then why not? There’s no particular reason to object to this feature, except for there not being enough resources to do everything, so things have to be prioritized. Such is life
Such an option would be nice. But like Saboteur said, I already got an extra tool for that. I would not need it if Renoise would offer that function tho.
Don’t worry, the current size of the to-do list would probably occupy Renoise versions up to 5.0