Adjust the other end of a visual selection

I think this would allow for the visual selection feature of vim to surpass the efficiency even of the mouse by providing an ability to "switch" the current terminus of the selection:

Illustrated (The | shall represent the cursor (Vim has it operate at the left-side of the character it is on) and [text] represents selected text, just pretend they take up zero width. The background of the space between [ ] looks grey, and the character immediately following the | is green):

Start with

Some |text here
Some second line of text
Some more text in the third line 

Press v2j; note the m character is included in the selection (it is highlighted by the cursor now):

Some [text here
Some second line of text
Some |m]ore text in the third line 

Press 10l:

Some [text here
Some second line of text
Some more text |i]n the third line 

It is at this point that I might decide I wanted to start selecting from a different location. e.g., including the "Some" on the first line.

I've got no choice in a typical editor/IDE. I probably would have to move my hand to the mouse, it's usually too painful to select text using traditional methods, the use of word hopping via Ctrl and page-up/down does help somewhat, but no matter what, I've got to commit to one of my terminating points of the selection before I start the selection.

So in Vim I'd love for the ability to take my current state and bring it to this by hitting a mystery binding:

Some [|text here
Some second line of text
Some more text i]n the third line 

Then I can just hit ^ or <Home> (both do the same in this case where there is no leading whitespace) to turn it into

[|Some text here
Some second line of text
Some more text i]n the third line 

Say I change my mind again, I want to adjust the other end!

[Some text here
Some second line of text
Some more text |i]n the third line 

Hit e:

[Some text here
Some second line of text
Some more text i|n] the third line 

Beautiful! I can do whatever I want next with this selection now.

So what's this mystery binding?

Also, even more potentially efficient would be a set of alternate bindings for some of the most-used movement commands to another row of keys, and these would (when in visual mode) always move the other end of the selection. So in that visual mode selection operation, if the movement keys for the other end of the selection were set to "yuio" (probably not a good choice since we kind of need y but just bear with me) we could have typed

v2j10l5ye

rather than

v2j10lX^Xe

Hey you know what, that's not even that much of an improvement. Just gimme that X feature. 🙂

The perfect answers that I'm looking for:

• Hey, look up :help some_awesome_vim_feature_that_just_does_this
• Hey, look at https://github.com/awesome_user/vim_plugin_that_does_this
• Hey, look at :help vimscript_functions_that_allow_mutation_of_visual_selections

I'm pretty new to this fascination with Vim so I am very green when it comes to Vimscript, and honestly I'd like to stay away from trying to learn yet another language, so hopefully I won't be forced to build this as a plugin.