While the conversation is still going on reviving multi-platform/mobile clients, a potential way to offer a broader range of compatibility is implement an XMPP server alongside the MSNP server. This means that any client that supports XMPP/Jabber (on pretty much any platform) can interact with the server without needing a compatible MSN client. Also, this would open up potential for a web-based client without reinventing the wheel, since there are open source web-based XMPP clients.
The main downside of this is that some features will not be compatible do to the differences between the two protocols. Another downside can of course be performance and the load on the server.
Thoughts on this?