i think you make some good points for better tuning in Renoise here. you should also be applauded for stating your feature requests so clearly, and accompanying them with mockups as well. really well done. i agree with you that it would be a good thing if the Renoise devs would consider implementing something like this.
the only thing i would want to a add to this is the combination of this with other often requested features, some of which are said to be in the pipeline for Renoise development. the main thing i am talking about here is the a future .xrni rewrite. there are a people having issues with the way instruments are currently set up in Renoise, and i can imagine the devs wanting to tackle that first before going into tuning, especially since if they do tuning first that would simply increase the amount of stuff that needs to be rewritten. so i think it should be done the other way around: first the instruments, then the tuning.