What is the exact behavior you'd like to achieve?
First I assume that you wish to have all the lines in reverse order all the time.
Note that in my opinion in most of the cases this would result in a terribly unusual and counterintuitive (if not straight broken) behavior, possibly something you'd give up using pretty soon.
cat'ing a text file would show its lines from the bottom to the top, not the direction in which you normally read text. In your favorite text editor and viewer the lines would also be reversed. In applications, their top bar would be at the bottom and their bottom bar would be at the top. In alsamixer the volume controls would hang down from the top. Box drawing characters (e.g. in alsamixer, midnight commander etc.) would fall apart at the corners. The Up and Down keys would walk the cursor in opposite direction in many apps.
This can be achieved by modifying your favorite terminal emulator's source (or VTE in case you use a VTE-based emulator like GNOME Terminal).
Basically the terminal emulator tracks the logical contents (which character cell contains what letter with what graphical attributes), and converts them to user-visible pixels (nicely rendered glyphs). This would need to go upside down. I'd look for the places where conversion between the character-based and the pixel-based coordinates happen, which is all the places where a multiplication or division by the cell's height occurs. These formulas would need to be adjusted. For example, if you see a
y_pixel = top_padding + row * cell_height, it would perhpas become an
y_pixel = top_padding + (number_of_rows - 1 - row) * cell_height, or something like this.
In VTE, super smooth scrolling (per-pixel scrolling with the touchpad), plus the way the extra bottom padding (in case of non grid aligned, e.g. maximized window) is filled with contents upon smooth scrolling will cause you extra headache.
Once you get the basic rendering done, you'd also have to make sure that mouse events that are sent to the apps are properly flipped, and so are the mouse events that track the selection. The scrollbar should also be flipped.
As a second step, you might want to either add a menu entry, or introduce a new custom escape sequence (probably a new DEC private number) that lets you toggle between the standard and this upside down behavior. Note that changing the mode would immediately flip everything (all the onscreen contents and history) upside down or back. It's handy to be able to restore the original behavior, especially if it can be done automatically in a wrapper script in front of let's say your preferred editor. In case of VTE and a VTE-based emulator, a graphical menu entry would require a new API between the two components, so it's one more reason to go for an escape sequence instead.
If you want to have something more fine grained than this, e.g. each command's output to appear in "normal" order while the sequence of commands is "upside down", then it becomes a magnitudes more complex story which cannot be done in the emulator on its own, it would need to get help (via newly designed escape sequences) to know which logical parts to flip. My personal recommendation is to forget it, I don't find it reasonably doable.