[docs] Update the ROADMAP

[oliviertassinari]

cc @mui-org/core-contributors.

Live version: https://next.material-ui.com/discover-more/roadmap/

[mui-pr-bot]

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thanks

[oliviertassinari]

Thanks for the reviews.

[ezhlobo]

Just wonder, why typescript over performance?

[oliviertassinari]

@ezhlobo Because more people asked for TypeScript.

• Our TypeScript effort is lead by: TypeScript demos #14897, it should provide us a better TypeScript support than a library written in TypeScript that has JavaScript only demos. It's a community-driven effort. I won't require too much time from the maintainers.

• Regarding performance, we have these interesting leverages:

  • [Table] Use makeStyles over withStyles #15023
  • [styles] Go back to index counter #15044
  • [List] Memoize context value #14934

  Our main bottleneck is the styling solution. Improving it requires a lot of R&D from the maintainers.