Side loading is possible but it's only for enterprise scenarios (I think the PC has to be on a domain etc.) Or have a developer licence. But that would still only be metro apps, not desktop apps.
latest when the desktop has disappered, you will be able to install it. I don't belive that this will only go for enterprise as this would cut the market.
The latest Google Chrome developer preview version can run in Metro mode when it is the default browser! Why isn't this breaking news? It is desktop software running inside Metro. Full support of snap and Charms features. No Windows Store download needed.
I genuinely don't know, I'm just asking. Does the DP of Chrome really represent Desktop software running in Chrome? I assumed that they just made Chrome have both the Desktop and Metro implementations, just like IE10 in Windows 8. In that case, it wouldn't really be Desktop software running in Chrome; it was designed (changed from previous versions) specifically to also run in Metro as well as Desktop. I interpreted the original question to be more of a general, i.e. "Is there a way to get software which currently only supports Desktop to run in Metro?" Maybe after RTM someone will make a Metro app which is designed to run any Desktop app inside it. I'm not sure what all this would achieve. I think that in this way, a Desktop program running in Metro will be pretty much just like the Desktop version except a few things, like that by default it would run in full-screen like other Metro apps, with the exception of how MS said they are going to make it so you can run Metro and Desktop apps side-by-side. Maybe a few other general Metro features, but I doubt if it would support any features specific to the app it's running... Unless someone also makes Metro front-ends for specific apps, or the aforementioned idea of a general Metro front-end for any Desktop app supports/contains definitions for specifically supporting certain apps. It could be Open Source (or not) and maybe support user-contributed definitions for specific apps.
The DP is Chrome for Desktop and Metro in one installation. If you set Chrome as the default browser, the Live Tile becomes a Metro Live Tile just like IE10. And IE10 Metro does disappear and change to the desktop version only. Chrome is the Desktop software with a different skin (larger buttons, different menu, no windows, only full-screen). It has Flash built in and full support of all Metro features (Snap, Search and Share Charms). The question is, how did they do this? Is this only possible for browsers? If not, every other developer could easily port their desktop software to run in Metro. Changing the skin of a complex software is easier than re-code everything in WinRT. Think of Photoshop could run as a Metro app... This is very interesting, IMO!