Will Power Nap be supported for earlier MacBook Air computers?

No.

As of right now, it is only available on the newer models. However, no one knows of Apple's plans and, if it is technologically possible, Apple may decide to release a firmware update for the older models.

This is what happened with internet recovery. It was only available on 2011 models, but firmware updates were released for some of the older models. No one knows if Apple will do this for power nap, but it is possible.

There is almost no chance whatsover it will be available for pre-2011 MacBook Airs since earlier models also supported HDDs. If there was a way to update the firmware in those then the recent SMC firmware update would have been availalble for those models. It would take a hardware update to make them compatible.

I thought all Airs only supported SSDs? Or at the very least the ones in 2010 were SSDs. As for whether or not they would be able to run the same firmware update, I'll have to take your word on that since I don't know how those work in detail.

No, earlier MBAs offered a choice of a larger HDD or a smaller SSD and have a different chipset than the later MBAs. And the MBPs don't even offer Power Napping in the 2012 models except for the Retina model, which does not at this writing have the firmware update.

Ah you are right. But I just looked it up and it seems that 2010 models were SSD only? So therefore it is possible that a firmware update may be able to enable powernap?

No, as I said if Apple was going to have a firmware update for the pre-2011 MBAs it would have been included in the recent update. Most likely the 2010 used the same controller chipset as the prior models and they are not updatable for use with Power Nap. The only way to update them would be to update the chipset.

Right, but what I am saying is could it be possible that the firmware update for the older models is still in development and/or they are not sure if they want to issue one for the 2010 models yet? Or is it technologically impossible that the machine can be updated through a software update to include this functionality?

No, they would have done them now if they could. There is nothing in the chipset on the older models to update. You would have to update the hardware first.