Auto Open Recent Environment on Starting Dream Maker would be a user friendly option.
When I open Dream Maker, I am usually going to work on my most recent environment. I think that for most users, this would often be the case. It would be user friendly if the most recent environment would automatically load when starting Dream Maker.

Let's keep it an option that by default is unchecked.
I could see this being objectionable to some users, though, so I think it would be better added as an option. Perhaps there could be, in the File Menu of Dream Maker, a place to checkmark "Load Most Recent Environment on Starting Dream Maker." By default, I imagine it could be unchecked, so as to keep the same behavior users are accustomed to, but allowing many users to take advantage of the convenience of the option.

How this option could function:
When loading Dream Maker by clicking on a specific environment from the Pager or from Windows, the selected environment should of course be loaded. But, if Dream Maker is launched independent of any environment (for instance, by opening Dream Maker using the Pager), then Dream Maker would see if the "Auto Load Most Recent Environment on opening Dream Maker" box was checked, and if so, the most recent project would be loaded automatically.