Goal: I want to find SDR software that supports keyboard shortcuts, and is most feature rich for raspberry pi. An option to program custom plugins will be an added advantage.

A few of the available options for raspberry Pi.

GQRX : GQRX is a general-purpose software-defined radio receiver that works very well on the Raspberry Pi, especially for the more powerful versions like the Raspberry Pi 4.  

RTL-SDR: While not strictly a software, RTL-SDR is a cheap USB SDR receiver that is widely used in the hobbyist community. Software to run RTL-SDR on Raspberry Pi is plentiful, including the rtl_fm command-line tool.

CubicSDR: CubicSDR is another software option that provides a graphical interface for SDR operations.

SDRangel : SDRangel is an Open Source Qt5 / OpenGL 3.0+ SDR and signal analyzer frontend to various hardware. It's more geared toward advanced users and offers a wide variety of features.

SoapySDR: SoapySDR is not an SDR application per se but serves as a SDR data manipulation library that can act as a middle layer between your SDR hardware and the software you use to process the radio signals. Many of the above-mentioned software options use SoapySDR in the backend.

GNURadio: Although complex, but it has a lot of features, and can be customized. It might me a good choice for this use case.

FreqShow: Its simple SDR software with options optimized for touchscreens. 

Now, I am looking for something that I can be easily customized.

right now GQRX and SDR++ are on top.

do share in comments if you feel a better SDR option