First of all let me just say, I am a big fan of Audacity and I want you to know that before the criticism starts. Audacity is a great audio editor, I think we all know this and it’s been around a long time to the point it has become a staple of the Open Source community as the go-to audio editor and an example of how great Open Source can be.
With that said, the problem of Audacity is that it looks like a relic stuck in time. Even the modernization of the look, doesn’t look modern. This is not to say that the design and branding was always an issue. The issue is that design trends have a lot over time but Audacity hasn’t.
The current version of Audacity  looks better than the previous versions, sure but the differences aren’t that much. This is very apparent when you compare the design of Audacity right before this “modern” version was made to the “Classic” theme  and then compare the Classic theme to the “Windows 98” version. 
The differences between Windows 98 to Classic is almost unnoticeable. If you move the toolbars in the Windows 98 version then its essentially the same. You could say “yea thats why its called Classic”. The issue is the difference between “Classic” and the current design is also not much at all. There are some icon changes and some slight color alterations on the timeline / canvas. That’s it.
There’s some good news though. . . no, Great News
I know this sounds like a lot of criticisms but there is a gigantic upside to this. There are MANY people in the Audacity userbase who are passionately fans of Audacity and also happen to be Designers . . . I am one of those people. There are also many examples of people making Audacity modern over the years that can bring inspiration to what the new Audacity could be.
higorsm25 from DeviantArt created a nice modern dark mockup for Audacity in 2015. 
madis posted a nice improvement to Audacity on Ubuntu here on the forum just a couple months ago. 
I am not saying that these themes should be adopted necessarily but that they are good paths forward to make Audacity not only a staple of the Open Source community but to invigorate a lot of people to be excited about Audacity and it’s future.
Additionally, I think that a new branding for Audacity needs to be adopted for modernizing the software because the current logo is improved from the previous states but it has the same issue that the software itself does, stuck in time. Good for its time but needs an update.
WedzMantra’s idea for updating the branding  is something I think is pretty well done. The modernization of it is nice and clean while still feels like Audacity to a degree and I like the A in the center merged in with the waveform. It’s a nice design concept. I am not saying it is perfect and should be adopted outright without adjustment but its a great start on the path of modernization.
I have seen many people make comments negatively towards Audacity solely based on the design of it and even in some cases refusing to try it thinking its not active anymore. This is very wrong on their part yes but that perception is there. Presentation is very important and I appreciate the fact that the Audacity website has been somewhat modernized but the program itself needs that too.
I can absolutely guarantee you that a hype train will go full steam ahead with a modernization effort in the design of the software alone. Do it in an all-encompassing approach with the branding and etc as well and you will have so many people talking about it you’ll have to pinch yourself to make sure its real.
I would be happy, no thrilled to help make this happen and bring Audacity to a presentation state that matches the awesomeness of the functionality it has. I am open to discussions for making that happen if the team is interested in making this happen. I also am a Podcaster and YouTuber so in addition to the Designer / Marketer value I also have the possibility of starting that hype train I talked about.
I apologize for the novel I just wrote but hopefully you see that as a sign of caring.
Screenshots for reference:
 Audacity on Windows 98 (circa 2004)
 Audacity “Classic” (circa 2017)
 Audacity on Windows 10 (circa Now)
- Archive.org is the source of the old screenshots