Carries as Supports

You have got a point, but pl could still probably be a stronger carry than she is.

Basically, I think any carry with disables and (sometimes) scaling abilities can do well as a support: Sven was a pretty common support some time ago, Naga Siren became one after the nerf. Others Heroes that could fit in the 4 or 5 role are Skeleton King, Chaos Knight, Dragon Knight, Spirit Breaker, Gyrocopter, Slark and maybe even Lifestealer: most of them can get easily fed with a good roaming partner and start snowballing; the others can jungle in the downtime and grant a gold lead to their team.

Unfortunately there's no reason to support with Phantom Assassin, Faceless Void, Spectre or Anti-Mage since their contribution as a support would be almost non-existent.

The flexibility in those heroes makes them viable as either, even though I'm simply restating that, it's the main point. Naga is great because of the flexibility and control she gives the team, her net is amazing for locking carries in place (magic immunity or not). Alch, Doom, and DK are great because they can roam, net kills, and farm fast. Want that fast Mek? All three of them can get it swiftly, and have much more staying power than hard support heroes.