There's been a few announcements recently that the upcoming version of SQL Developer will include database table modelling features. It seems to be a little know fact outside of JDeveloper circles that JDeveloper has had "offline" table modelling for sometime. The 11g release has expanded upon this feature set to include more options, that in turn make it (more of) a viable option to replace Oracle Designer physical database modelling.
(I suspect the upcoming SQL Dev modelling features just come from JDev anyhow, but I can't confirm this).
In particular in the 11g release we now see that offline database objects have support for normal tables, external tables, index organised tables, temp tables and so on through the radio group at the top of the screen:
In addition for normal tables when selecting the Storage Options button under the Table Properties subnode, we now have the full gamut of storage clause options for the table we're creating:
I know of a few Oracle sites that are holding onto Oracle Designer purely for its physical database modelling features only. Through the latest release of JDeveloper we can see there is the potential to drop Designer all together and go for the free JDeveloper. Now only if those sites could drop Oracle Forms too ;-)