SWT doesn't run on top of GTK 3 (latest and greatest ) but work is ongoing. Last week was a really productive one getting us to the state of less than a hundred compile errors (well, some are warnings actually). Not only that but we are down to 75 as of today. A number of others are pending reviews in bugzilla giving us hope that speed should not decrease.
Here is the list of all the GTK problems we have identified for now. Be fast and pick one (check the tracker bug first), open a bug and block the tracker so we know someone is working on the issue. There is still time to add your name to Thanks list. If you want to help out checkout swt from git and when building natives instead of the plain `sh ./build.sh` do `GTK_VERSION=3.0 sh ./build.sh` the list of errors is what's still pending. Nothing else but code counts as help for now! There should be semi-regular updates on the state from now on.
Big thanks to SWT project members for making me a committer to speed up the work and to my teammate Anatoly Spektor for his hard work on the topic in the last months.