I'd be surprised if that happened. If they can get the console out at $400, then don't expect them to release a model that costs more than that just so that they can have a BC model available. I expect them to keep the PS3 pricing backlash in mind with the PS4. The PS3 launched with a $500 model also, but all you heard about was "FIVE HUNDRED AND NINETY NINE US DOLLARS!". That higher tier price didn't do them any favors.
There's a big difference. PS3 as intended was the 600$ model (with HDMI video output, Wi-Fi, cards reader...even the chassis

). It had all the features that Sony said the PS3 would be defined by. 20GB model was just the PS3 gimped in every possible way in a desperate attempt to make it cheaper.
It's obvious that consumers notice the trick and there's backlash.
What if they do things backwards?
The entry price model is the product as intended and then extra features are included in a more expensive model to justify the extra price.
In that case I doubt that people would complain, infact traditionally they haven't.
With Vita for example people don't consider the entry price to be the 299$ of the 3G model while the Wifi model is gimped, the Vita is the Wi-fi model and then if you want 3G as an extra you pay the extra 50$.
It's all a matter of perception and how a company spreads its message.
With PS4 it makes sense to design the product around the 400$ launch price point.
Then if they want to make a more expensive model with a bigger hard drive, a DVR and/or hardware based PS3 BC they can certainly do it. If people think that hardware based BC with a previous console (so not the console they're actually buying) is worth it, it makes sense that they recognize that value. That also doesn't exclude that non hardware BC is implemented in some form in the basic model.