Plugins imply an audio architecture for the plugins , well to plug in to. The code base for that my friend is huge and is usually sits on top of monolithic OS like MacOS, Windows or Linux. There are some keyboards Yamaha and Korg for example that run Linux as an OS, embedded OS to host the audio engines and then the modules are basically
What is happening nowadays is an IR loader and also DSP but it is not a plugin architecture. And it is already here. It started a long time ago, Fender and Vox have already done it and the sophisticated ones like Kemper and the like. In the bass amplification world, this is simply not cost effective and what is happening is you are seeing a lot of preamps that can load IRs and DSP to emulate amps, cabinets and effects. But you can't bring in Ampegs SVT Suite plugin directly because #1, not enough CPU horsepower and you would need a display and mouse touch screen to control the VST plugin
Plugins in the strict sense of the word work with DAWs and they can do many things not just emulate amps or outboard gear but play samples of instruments (native Instruments for example). VST is the word that you have to become familiar with Virtual Studio Technology and this was release by Steinberg who created the DAW Cubase. It is possible to have hardware that can load VSTs and usually that is done by the keyboard companies. Roland , Korg etc. The development cost for this is huge