What problem does this solve or what need does it fill?

This allows fade-in fade-out transitions for UI bundles, and setting the overall transparency of UI bundles, which I think is useful in many games to unclutter the window when it's not really important (but may be needed) or as a configuration in games for players who wish to unclutter their view and see more what's going on.

What solution would you like?

To be discussed.

What alternative(s) have you considered?

For my own game, I am considering trying to do pop-in pop-out animation with Transform. It allows a more cartoony transition, but for others this might not been what they prefer for their game theme.

It's possible to change the opacity of TextBundles and background colors but that's a major hack and can't be used with ImageBundle

Additional context

https://developer.mozilla.org/en-US/docs/Web/CSS/opacity