This new "interface" already exist in ..... arranger keyboards.
You can buy a relatively cheap one for around 150$ (or used one on local Craiglist for around 50$) that has much much better quality / and live control than iReal Pro. I truly love iReal Pro and just bought it a few days ago as it allows me to create backing track on the go (anywhere) with my tablet, and I can play an other instrument and / or sing along with it.
I could do the same by recording the backing track I play on arranger keyboard.
Here are the pro and con of both:
1) arranger keyboards: much better sound, live control,
a) if play live, cannot play another instrument, but can sing
b) if pre-recorded, it's hard to keep track where you are in a song (blind play / sing along)
c) not very portable even with portable keyboards

2) iReal Pro advantages:
a) one can see where you are in a song, hard to get out of sync
b) extremely portable
c) can create backing track anywhere (even in a flight, using a head phone, surrounding people will hear you humming along !!!)