Eye of Skadi as replacement for Heart of Tarrasque on meele carries?

And I wonder who is that?

The only character that gets five times the benefit of any item with stats on it, provided he also has Aghanim's Scepter: Meepo. Each clone gets the full +25 agility, and its direct translation into +25 damage, which means a total of +125 potential damage when focused on a single target in a fight or when tearing down a tower.

Oh, and I wouldn't say it replaces heart on Meepo, but it can definitely supplement heart to turn Meepo from clay into a brick. 3300-health clones and a 4000+ main Meepo are pretty sturdy.

Eye of Skadi? I remember that some months (almost a year, I think) ago it was core on a hard carry Sniper build I saw in a competitive match, even though he was picked very rarely.

Talking about melee carries, I think that the slow could be useful but there are other orb effects which can grant a lot more benefits ( Diffusal Blade and Desolator, mainly) or there's just no reason to buy it. But anyway, I think it is very useful on semi-carries or gankers such as Bounty Hunter and Slark: if you need to be more durable this is surely better than a Heart of Tarrasque; even though a Satanic is sometimes more convenient (against Lifestealer).

Skadi is a real option for substitute. Especially if an agility carry.

Eye of skadi compared to Heart of Tarrasque:

skadi builds better
+25 dmg (if str. -15dmg)
+25 attack speed
+575 mana
+3.5 armor
+1 mana regen per sec.
-335 health
-175 more gold

IMO Skadi is definitely an aggressive substitute for heart, and the speed slow will effectively grant more staying power if attacking the carry.

In my experience, the hero that I always love to get Skadi on is Slark. Slark is really stat deprived, and doesn't mind picking up an Ultimate Orb every now and then. He also is mana starved as well as exceptionally squishy, so he doesn't mind getting an early Point Booster. Orb of Venom is just a cheap item that can boost any melee hero's damage, as well as give a slight slow. Slark also prefers to get tons of quick, but weak attacks on a single target, so Essence Shift can kick in. In a 1v1 gank, slowing the target to a crawl, in addition to pounce and Shadow Dance gives you such a long window to easily steal 20+ stats.

I always get a Skadi over something like a Heart/Bloodstone on Slark late game to boost his survivability. You can even focus his entire item build around getting it as soon as possible. While I dont recommend rushing Skadi, often I get an early orb of venom, followed by a point booster, and then a mid game damage item like Yasha before finishing Skadi.