I'm still building new frontend UI with Typescript 2.x, Bootstrap 4 alpha, Pixijs 3.x. I don't particularly care about flags in code dependencies, and if they're a problem to upgrade I'll use the old version too. Does it matter? A UI just needs to work, ideally forever, and it's all javascript in the end anyway. It'll work the exact same 10 years from now. Serverside code is a different beast and you can't avoid upgrading Node or PHP, or migrating to MySQL 8. But only very occasionally does this present the opportunity or sufficient reason to upgrade frontend code.