Since Xbox One and Wii U had their own backwards compatibility that leads to the PS4 the only current gen system without the feature  Sony adding the feature would give them loads of cash! Why?... Well if they released backwards compatibility.. I would sell my PS3, and purchase 3 PS4 games!!!! Game sales would totally go up for the PS4 Library by the thousands of people selling their PS3s to buy more PS4 games! and also people would totally buy PS4s too!  What are your thoughts???

Yes, Sony would likely sell a lot more consoles but developers would sell a lot less next gen games. If people can just play their old library for weeks on end then it's less likely they'll buy new games just for something to play.

I hope Sony goes to backwards compatibility, PSNow just simply isn't going to work for them like they wanted in the long run. Really, I would rather buy a used PS3 than use that service.

I doubt the increase in sales would be enough to cover the cost of adding the feature (if they even could). It's far too late for BC to matter in any meaningful way.

PS3 BC is imposible

Then I'm not sure if you entirely understand the nature of PSNow. It was never intended to be a BC solution and I wish Sony had marketed the service differently so people would understand this. The primary prospect of PSNow is its ability to transcend the closed platform loop that we know as PlayStation. It's ideal use allows it to be played on - your PC, your smart phone, your TV, your cars GPS screen... Without the need for a PS3 or PS4. 

I think behind the scenes Sony will eventually push PlayStation as a service rather than a piece of hardware, and this slow but steady adoption will make that transition as smooth as possible.

Proof?

PS3 is the proof

So you have conjecture.

Truthfully not many people here are qualified to speak on the matter. But I think it could be possible. 

For PlayStation Now to have a viable future, Sony has to get everything running on X86. That means they basically have to make official emulators for PS1, PS2, and PS3 that are work on PlayStation 4. There is no way they can afford the cost of running server farms for multiple platforms, so in time this will come. I am not sure when it will come or how it willbe rolled out, but I would guess Sony would not roll it out until it is 99% compatible with all past PlayStation games.

In the future I don't see Sony going full stop with new PlayStation consoles. From here on out, PlayStation will be an ecosystem on X86 and running on Sony's OS. All PlayStation games will run native on the devices with PS Now being an alternative for console owners, and a way for people without PlayStation hardware to enjoy PlayStation software.