I don't think Viktor would benefit from Runeglave like Ezreal has.
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Runeglave converts Ezreal's Q into a Magic Damage attack, which makes it scale with Magic Pen. Viktor's Q already converts his next auto into a Magic Damage attack, so this adds nothing for Viktor.
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Runeglave gives Ezreal a source of AoE waveclear that isn't his ultimate. Viktor already has his Laser for impressive waveclear.
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Runeglave gives Ezreal an easy way to get mana back (Q over the wall to Raptors). This convenience is lost on Viktor, who has to get vision of the raptors, then Q-Auto at a much closer range to get mana back, likely loosing some HP in the process at early levels.
In the end, I think that Lich Bane is the better fit for Viktor. It gives him movement speed, which he needs to get into range to use his Q, more AP, and has better single target scaling. The advantages you list are more general to getting Smite rather than specifically getting Runeglave.
As for slowing, while
steals 20% of the target's speed, you could alternatively go for
, slowing the enemy by 40% for a little longer and from a further range, getting AP, movement speed and CDR for your trouble while saving a Summoner Spell.