Yeah, running ~/.bashrc is tough, and I'm not sure even Oil will get to it. Not only do you need parsing and execution of the bash language, but you also need builtins like bind and set -o vi (i.e. see "help bind").
Maybe bind is easier than I think; maybe it's just a few readline calls. I haven't looked into it.
But also, I noticed almost no shell scripts use extended globs like @(foo|bar), whereas the bash-completions package uses them EVERYWHERE. Completion scripts are almost like a different dialect than other shell scripts.
If you want to source /etc/bashrc on most distros, you're going to end up with thousands and thousands of lines of plugins from the bash-completions project.
The parsing is a big headache, but I think it forced me to learn how people use shell, which will benefit Oil.
It's been a full year since our alternative shells thread... might be time to revive it and see what's changed! Congrats on the Elvish releases!