what is really different from a safety perspective than a lineman or back peeling back and doing this vs. the guy started from the outside doing it.
Generally, I think the outside guy going back in, i.e. the current illegal block, occurs earlier in the play, and the blockee does not have a chance to see the block coming; hence, can not try to avoid it or brace himself.
On the other hand, the lineman/back peeling back, i.e. current legal block, occurs later in plays, after a scrambling QB reverses direction. And the block is usually thrown against a defender in pursuit, who can see the block coming; hence, not blind sided.
BTW: How is the block on the video different from a tailback blocking low and in front on a defensive tackle rushing a dropback QB? Are do y'all think that block should be illegal as well?