This is already possible.
To enable this, use the "-i" switch while launching the second (and all after that) instance of the app.

No, it's about organizing tags into a taxonomic hierarchy. For example, tag "programming" will contain tag "c++". Now if you pick the tag "programming", all notes having the tag "c++" will be shown, they will all implicitly have the tag "programming" now (of course the notes having the tag "programming" explicitly will be shown as well). Combined with tag union, intersection, and subtraction (Shift, Ctrl and Alt clicks), it will give great power and flexibility while being hopefully not very hard to use.

I agree that it definitely would be more convenient to have just one place to discuss features.
Unfortunately at the moment I can't move all the discussions over to UserEcho, because it doesn't support attaching files, images and rich text formatting, all of which is often necessary in feature discussions. This is why UserEcho has a more official status of being the public roadmap, and the detailed discussions of the features should happen on the phpbb forum.

UserEcho guys plan to add Markdown syntax support soon, so it is probable that the whole "Feature Requests" and "Bug Reports" forums will be moved here. The general forum will stay since it contains a lot of topics which are neither "Thanks" nor "Questions".

Thanks for all the kind words! Your story is very interesting and I kindly ask for your permission for using it in promotion materials. I'm wary of the app becoming bloatware, this is why I prioritize features that are more organic. In this regard UserEcho helps a lot: I can see if there are users which would prefer not to have the new feature in exchange for simplicity/resources etc. This is why all the features where more than 20% of the votes are downvotes will be made optional, no matter how high its score is.
Thanks again and hope you'll enjoy using CN.