I'm pretty confident I don't want this. I'd like to be proven wrong, but there was maybe a couple of cases among hundreds when perfectly working UI was actually improved instead of fucking broken by "getting a new look".
What I actually would like to be improved is how the data is represented internally. Let's face it, it has been a long time since Wikipedia has become the largest and most accessible knowledge base in the world. It was made simple, which is a part of why it is successful. MediaWiki is pretty much a blogging engine, article content and structure is restricted by the guidelines only, not by the engine. This is good, and at the early stages it was the only possible solution, since there is so much that can be useful in an encyclopedia article.
However, now we know a lot of patterns of how data represented in different articles is similar. But wikitext is still basically just a human language with a bit of markup elements. Sure, there are templates, which are slowly improving over the time, but still, it's petty much a collection of free-form blogposts. There is almost no way to separate data from the representation (i.e. to have a table contents as a csv, with a template assigned). There were some attempts to make it possible, but querying (or modifying) data automatically is still very much a pain. A lot of it requires parsing, and (perhaps even more annoyingly) — pretty simple parsing. But you have to do that work for every single problem you have. Instead of, you know, to just query data I know there is. In fact, when you start parsing templates it becomes very clear very quickly, that they are vastly underused. Absolutely the same data, like years of life in bio-articles is still represented differently even in very elaborate and well-maintained articles.
Very little has been done in this regard over the last 10 years, I feel. And improvement does require a lot of work: looking for possible templates, promoting generic data representation among contributors, modifying wikitext to allow for it, improving the API. It they are looking how to spend money, I'd rather want it to be this, because making a lot of data machine-accessible would be literally as huge, as making wikipedia human-accessible was about 20-15 years ago. Sometimes I need to open 500 articles to read a single sentence in each of them, and some python script could've done it for me in a second (a couple of seconds maybe, depending on how wikipedia stores and represents the data).