now that TEM2 is in Beta state and mostly done, it'd be better if you could play it to test all the new things before suggesting anything for TE4.
Read here for more details about what's already done in TEM2 : topic15-30485.php . There's a free demo for it like for TE2013.
However, if you don't have the time to try TEM2, your feedback and wishes from TE2013 are still welcome here, of course !

Legacy topic with ton of suggestions : topic15-15146.php (you don't have to read it, it's ok to suggest something which has already been suggested in the past

EDIT April 2020 :
At this point, it's highly recommended to have played TE4 at least a few hours before doing any suggestion, as there are already a lot of deep core changes, so making suggestions from your TE2013 experience will make little sense with the current TE4 state.
Important Note :
This is not a feedback topic for TE4. ie: do not post stuff about tuning little things or talking about aspects of features already implemented in TE4. If it's about a change from the latest version then post in the "TE4 Comments" topic instead, else just create your own new topic, it'll be fine.

I'll move your post into the current TE4 feedback topic if it belongs there, or even in its own topic. The idea of the suggestion topic is to be as short & clear as possible, so I can re-read it when the need arises ; ie: it's not for discussions (although I often try to comment your suggestions so you get an idea if they are possible to implement or not

In other words, do not post here about tuning, balance, modifications of existing stuff or bugs.
EDIT July 2021 :
You might want to check 1st the features on the Roadmap here : topic15-33253.php .