There is a fair amount of historical information about how the interface evolved to the state it current is in terms of Clear and Exit at https://www.stoutner.com/privacy-browser-design-guidelines/. I would recommend you take a look at what is written there.
In general, I am opposed to adding a general Clear and Exit to the main screen (beyond the Clear and Exit that already exists on the main screen when you close the last tab) for the following two reasons.
1. There is no obvious place to put it on the main screen that take up too much screen real estate.
2. Every place I could think of putting it on the main screen or any type of gesture would have the unacceptable negative effect of having lots of false triggers. As described in the link above, I am particularly sensitive to GUIs that are prone to doing something that user didn't intend. Irretrievably closing all open tabs when that is not what the user intended is an example of something that any implementation must avoid doing.
If you can think of an implementation that addresses these two concerns I would be interested in hearing it.
Each feature request should only discuss one issue. Your second idea is interesting. I would recommend you open a new feature request to discuss it.
There is already a fair amount of information written about the timing of the 4.x release. I would recommend you read over the roadmap. If that doesn't answer your questions you can post in the forum and I will be happy to respond.
https://www.stoutner.com/privacy-browser-pc-roadmap/
https://redmine.stoutner.com/projects/privacy-browser/boards