This topic resurges periodically. Allan (the main developer of TextMate) has stated the projects feature has not been implemented in TextMate 2 on purpose in favor of a completely filesystem-based approach. From his comments, it is clear that putting projects back into TextMate 2 is, if it is on his todo list at all, on the very bottom. After all, TextMate 2 is still an alpha, and there are other things that need to be fixed first. So I wouldn't hold my breath and wait for projects to return any time soon. Perhaps they'll be back in TextMate 3, who knows ;-)
Even though TextMate 2 is open source now, no one has volunteered (yet?) to add projects support. Right now, your best chance is to adapt your workflow or to continue using TextMate 1.5.
If you search this mailing list, you'll notice that I'm in the same boat as you, to me projects was what made TextMate 1 so appealing to me. There are a few things I've done to adapt:
(1) I've given up on symlinks, I open several editor windows instead.
The reason is that while symlinks work for single files, they don't work well for folders: if you create a symlink to another folder, you will not have a small triangle next to it which you can use to expand it. Double-clicking it works fine, but navigation is more cumbersome and there is a difference in how to work with symlinked and non-symlinked folders. Allen has explained why it is not easy to make this work properly (you have to account for all sorts of eventualities), and I don't think fixing this is very high on his list of priorities. If it is fixed at some point, perhaps I'll revisit it.
What I've done instead, I keep open the linked folder in a separate editor window. Definitely less elegant, but it works.
(2) Use good .tm_properties presets
The .tm_properties file allows you to set presets for a specific folder. There is one »master« .tm_properties file and it is worth spending a little time to customize it. However, I rarely edit the .tm_properties file of a specific folder (e. g. to hide certain auxiliary files). I often resort to the Terminal to open files instead of using the file browser.
.tm_properties is definitely more powerful than project presets in some respects, and perhaps if bundles make use if it (by editing the file or something), it could replace some of the functionality of projects.
(3) Use »mate .« to open folders.
Instead of »open project.tmproj«, I now type »mate .« to open a folder after navigating to it. I use git from the Terminal anyway, so I have become accustomed to opening folders like that. I keep several Terminal tabs open, one for each location in the filesystem I need (e. g. auxiliary files or documentation).
If you have more specific needs, just let us know. Perhaps there is a work-around.
Hope that helps.
Max