We meet biweekly; you are welcome to join, send me an email address and I can add you to the invite. As to areas where help is needed is plenty. I think that the question is where your interests lie.
Networking is definitely one; SwiftPM is another. Compiler performance is definitely something I want to look into. There is work for improving the packaging, adding more features, and of course my own pet things, e.g. tcrun (which would require some design work to improve the installer so that we can programmatically enumerate the toolchain, alter the installation, etc). VSCode integration, DocC, debugging, and soon COM are all areas. CAS is something that would be lovely to get some help with (there are a few items there that remain). If you want to work a bit across swiftlang and bcny items, improvements to the GHA based CI - which while sounds less interesting, is quite interesting! That would be altering the GHA builds (and build.ps1 potentially) to get PGO working.
I'm no longer convinced that this is the case. Yes, the file system is a little bit slower on windows, but it is not the cause of all of our troubles. We found that there are actual issues in Foundation, swift-build, SwiftPM that are a concern. In particular, we do something incorrect with handle inheritance which is unnecessarily slowing down the build.