It's worth investigating if legacy flexbox properties (display: -webkit-box) can be implemented as aliases of modern flexbox properties (display: flex).
Firefox does this, and I think Chrome might as well with their new layout engine.
For reference: https://compat.spec.whatwg.org/#css-property-mappings
They're not actually aliases; see https://github.com/whatwg/compat/issues/87.
line clamping is a RenderDeprecatedFlexibleBox only feature.
(In reply to zalan from comment #3)
> line clamping is a RenderDeprecatedFlexibleBox only feature.
See https://groups.google.com/a/chromium.org/g/blink-dev/c/SVD5wSqVwKU/m/eY28UiNkAwAJ for what Chromium has done there; essentially their deprecated flexbox implementation is actually their line clamp implementation (and only used in that case, and many of the properties no longer exist there).