Those products he mentioned like Mono are just direct clones of MS products, I doubt they'll ever overtake the original and instead seem to be a desperate attempt to find a small niche in the growing .NET world before they were left completely on the outside looking in.
Actually, as the platform itself has been standardized (ECMA 335), it is not the platform that is hard for them to create. The hard part is recreating the extra libraries, not part of either the CLI or C# standard that MS bundles with VS.
DotGNU is making pretty good progress. Their status on the libraries is available at Portable.NET Status Page. Mono has been working on this as well.
To some degree they will always be playing catch up--recreating the libraries as soon as MS puts them out. However, this isn't the impossible task that Win32 was.