This is a heads up about some of the things the Growth team is thinking about and working on with mediawiki.ui.
We're in the process of adding optional icon support for mediawiki.ui buttons, with browser support down to IE8.[A]
We're going to get rid of the text shadow on the default mediawiki.ui buttons.[B] It's distracting and doesn't increase readability. We don't use gradients in the colored buttons for similar reasons.
We need to do some tweaking of the design of the default mediawiki.ui button.[D] We're designing the second iteration of the anonymous editor signup invitation UI to A/B test.[E] When looking at these, you can see that the default mediawiki.ui button ("continue editing") almost seems disabled. We should talk about ways to improve on this design, such as darkening the text color or giving the default button a background color.
This may come up in the WMF UX team's weekly design review as well, but I wanted to give a heads up about these issues since the library is in MediaWiki core.