Our work to be done:

• Remove deprecated rules #5290
• Remove function-calc-no-invalid #4731
• Remove syntax option #5289
• Remove Node 10 from CI #5292
• Migrate to PostCSS 8 #4942
• Fix cache  #5309
• Remove DisableReportRange.unusedRule #4899
• Add overrides property to configuration object #3128 (minimum for customSyntax)
• Remove configOverrides option #5522
• Add customSyntax option to configuration object #4843
• Fix CodeQL warning in indentation #5128
• Improve migration experience to customSyntax #5301

I believe these are the steps to releasing a version without any security warnings.

Non-blocking work we or the community needs to do:

• Prepare for stylelint version 14 vscode-stylelint#233 - Prepare VS Code extension
• Help us prepare for the next major release of stylelint stylelint-scss/stylelint-scss#541 - Create and publish stylelint-config-scss-standard

Non-breaking nice-to-haves:

• Remove isInteger polyfill #5219
• Refactor via fs/promises module #5271
• Refactor *-no-vendor-prefix to avoid using autoprefixer #5293
• Refactor to lodash-es #5294
• Add all options to configuration object #5142
• Move to ESM #5291

Non-blocking limitations:

• Fix multi-line double-slash command comments #5348

Release:

• stylelint release Prepare 14.0.0 #5604
• stylelint-config-recommended release Prepare 6.0.0 stylelint-config-recommended#123
• stylelint-config-standard release Prepare 23.0.0 stylelint-config-standard#198
• stylelint-scss release Prepare 4.0.0 stylelint-scss/stylelint-scss#547
• stylelint-config-recommended-scss release Prepare 5.0.0 stylelint-scss/stylelint-config-recommended-scss#84
• stylelint-config-standard-scss release Prepare 2.0.0 stylelint-scss/stylelint-config-standard-scss#1
• stylelint-demo update Update to stylelint 14 and related configs stylelint-demo#270
• stylelint.io update Update to stylelint 14 and related configs stylelint.io#227
• tweet (announcement (links to changelog and migration guide) + thanks) (follow up with VS Code)

Node 10 EOL is at the end of April. A lot of the packages we depend on will shift to Node 12 (and ESM) around then (see #5198 and sindresorhus/meta#15)

It'll be a major release of stylelint, so it's an opportunity to roll in other breaking changes. If you've got an itch to scratch that's a breaking change, then this is the time to do it!

We should remove deprecated code, e.g. #4899 and all the deprecated rules.