Will there be only one set of DLL's for all the editions in 4.0? I must say it has been a nightmare having 2 sets of DLL's for v3.7 Standard and Community editions. This means managing multiple code trunks for the same custom extensions... even though they may be identical code. If there was only one reference for Standard and Community with certain features disabled depending on the license, it would alleviate managing custom modules and plugins.
In the Sitefinity API, there could be a property or method such as GetEdition that would return an enum of what current edition is running. This way, extensions can also disable certain features based on what edition is running. For the most part, all editions share a huge chunk of logic which is why this would make things easier I think.