Could visual-block show inserted text as it's being typed?

Originally reported by: **Ivan Brennan (Bitbucket: [ivanbrennan](https://bitbucket.org/ivanbrennan), GitHub: [ivanbrennan](https://github.com/ivanbrennan))**

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I realize this may be a big ask, but would it be possible to display inserted text on all selected (non-blank) lines as it's being typed from the visual-block state? Kind of like what `string-rectangle` does, though inserting rather than replacing.

To clarify, when I've selected a rectangular region ("C-v") in evil-visual-state , and I press "I" to insert text at the left edge of the region, it currently displays the inserted text on the first line, and only after hitting Escape does it insert the same text on all the (non-blank) selected lines. This is true to the Vim implementation, but it would be even better if it provided the full visual feedback by inserting text on all the relevant lines as you typed.

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- Bitbucket: https://bitbucket.org/lyro/evil/issue/710

Start by reproducing the behavior in evil-visual-state with a C-v selection, then press I and type before pressing Escape. Compare the current feedback with string-rectangle and the described Vim behavior. Done means inserted text is visibly shown on every selected non-blank line while typing, and the final insertion remains correct after Escape.

Written by the indexing model from the issue text.