What would I migrate to? Vanilla. It's less code, easier to use code, and if you progressively enhance it's more accessible a result. ESPECIALLY if like a smart person you make it work WITHOUT client-side JavaScript FIRST, then enhance it with scripting where and only as necessary.
Especially if you scrape the bootcrap off, with its riduclous code bloat, lack of separation of presentation from content, and PRETEND "responsiveness" that breaks down for anyone using a non-standard font metric, OR (you have a choice) flips the finger at same by declaring everything in pixels. There's a reason I tell developers to find a stick to scrape that off with before tracking it all over the web's carpets.
Dimes to dollars you could use half the code or less, develop it faster, better leverage caching models for faster sub-page loads, have it future proofed, and even be able to restyle it top to bottom without even TOUCHING the HTML. Aka a good chunk of why CSS even exists. ALL by kicking the framework nonsense to the curb.
All these "frameworks" people constantly tout as simpler, easier, faster, 'more productive', etc, etc generally do the exact opposite. They're more code, as much if not more work, and flip the bird at usability and accessibility for anyone who doesn't have the magical combination of perfect eyesight, perfect mobility, and desktop resolution screens.
Put on the big-boy pants and lose the training wheels.