The point of having it editable for the menu widget, unlike your contact form on a normal page, is because the form can't be added from any content section when used the menu. For your page, the [contact] shortcode is basically just a shortcut for the following code that you can also add manually into any page:
<form data-abide class=contactform>
<div class=honey>
<input type=text class=honey1 name=honey1 placeholder=honey1>
</div>
<div class=honey>
<input type=text class=honey2 name=honey2 placeholder=honey2 value=googooforgaga>
</div>
<div>
<input required type=text name=name placeholder=Name>
</div>
<div>
<input required type=email name=email placeholder=Email>
</div>
<div>
<textarea required rows=6 name=message placeholder='What's up?'></textarea>
</div>
<button type=submit>Send</button>
</form>
Not making this accessible for editing from some custom editor, is because
1) Unlike the menu contact form, it can already be added manually like in the above.
2) Requiring users to add all the elements above for a simple form, without making any typos, including the hidden anti-spam fields, is a challenge, and would surely cause problems
3) Since X3 does not include an automatic form-creator from anything form elements you add, it does not make much sense to require the code above instead of [contact].
4) Easier form creation- and integration will come, at some point down the road!! Thnx.