Performance-sensitive apps already do that (like VS Code, Atom). Most of the cost is in the javascript, caching bytecode lowers startup time a lot. Pre-rendering is not really practical, and painting is rarely the main bottleneck either way.
AFAIK the main performance issues come from chromium's vast size - browsers are complex machines and it's easy to hurt performance by doing something that looks reasonable at first, but blocks the UI. Being single-threaded doesn't help. But reality is, most of the time Electron apps perform really well, it's just that they have slower startup times, consume massive amounts of memory, more CPU than average, and are 100MB each.
AFAIK the main performance issues come from chromium's vast size - browsers are complex machines and it's easy to hurt performance by doing something that looks reasonable at first, but blocks the UI. Being single-threaded doesn't help. But reality is, most of the time Electron apps perform really well, it's just that they have slower startup times, consume massive amounts of memory, more CPU than average, and are 100MB each.