We've decided to ask the community what sort of radio would be more popular for a ~$30 RX-only SDR. Note that thus far this is only a hypothetical SDR that does not yet have any designs. We are just feeling for what's most interesting to people and exploring for future ideas which may not even be feasible at this time.
As always with engineering, there is always a trade off. It is likely that any low cost SDR can only be wide band, with basic RF performance, narrowband with good RF performance, or expensive.
Wider bandwidth: Currently the RTL-SDR allows you to see up to 3.2 MHz of spectrum live. Higher bandwidth (10 MHz or more) would mean seeing more of the spectrum at once without needing to retune, faster whole spectrum scans and the ability to receive wideband signals.
RF Performance: The RTL-SDR has an 8-bit ADC. While sufficient for many applications, in the presence of strong signals the ADC will saturate resulting in poor reception and signal overload. Higher end SDRs like the SDRplay, Airspy, LimeSDR etc use 12-bit or higher ADCs.
Frequency Range: The RTL-SDR V3 can tune from 500 kHz to 1.75 GHz. An expanded SDR could potentially tune up to 4 GHz or even higher.
If you're interested in other things, please comment on this post!