I converted my Webpack 4 based setup from babel 6 to 7 with no issues, yet. They did a good job on the migration guide. Take a look
babeljs.io/docs/en/v7-migration
Their package renaming was a step indeed.
If it could help somebody I updated my sample repo for my setup to Babel 7 / Webpack 4 on the master. The Webpack 3 version got pushed into a side branch.