I'm not familiar with all the implementation details of objects in C#, but the list of issues mixes runtime implementation details (object layouts) that should be fairly low effort to work around with actual language/runtime features (references, finalization).
In general though most regular C# code written today _doesn't directly_ use many of the features mentioned apart from references. Libraries and bindings however do so a lot since f.ex. p/invoke isn't half as braindead as JNI was, but targeting the web should really not bring along all these libraries anyhow.
So, making a MSIL runtime that handles most common C# code would map pretty much 1-1 with Wasm-GC, some features like ref's might need some extra shims to emulate behaviour (or compiler specializations to avoid too bad performance penalties by extra object creation).
Regardless of what penalties,etc goes in, the generated code should be able to be far smaller and far less costly compared to the situation today since they won't have to ship both their own GC and implement everything around that.
Part of the problem is you would need to fork the base class libraries and many popular nuget packages to remove any uses of ref/in/out, along with any interior references, spans, etc. The .NET type system has allowed 'interior references' (references into the inside of a GC object) for a long time and it's difficult to emulate those on top of WasmGC, especially if your goal is to do it at low cost.
It's definitely true that you could compile some subset of C# applications to WasmGC but the mismatch with the language as it's existed for a long time is painful.
Like I wrote, references could be managed with shims (basically a getter-setter interface per-referenced-value-type that's then implemented per-target type) and yes it'd be a painfully "expensive" variation, but for 90% of the cases those can probably be rewritten by a compiler to an inlined variation without those performance penalties.
My argument is that, code that goes on the web-side mostly would adhere to the subset, many of the ref-cases can be statically compiled away and what remains is infrequent enough that for most users it'll be a major win compared to avoid lugging along the GC,etc.
I wonder what language this GC can actually be used for at this stage?