I can't currently remember what it is called off hand on Vuze, I have heard it has it on the site, but never used Vuze, and I hate Vuze $$$. Tixati is wonderful, and had been my goto torrent program for a couple years now.
Anyway, the feature it should implement is this: take for example two different torrents with the exact same file (for some references some releases have a whole separate file, which has the same file, same size, hash, etc different torrent. I am not sure if I should post links to such things on here...
But sometimes neither one of them are well seeded, and I can often get parts of one, parts of the other - by stopping one torrent, copying it over, force recheck - start again, to seed them both, and complete both unseeded torrents. Over the last year, I have probably already saved a couple/few dozen torrents until no active leeches like this, and also got my files complete.
What Vuze has from my understanding, is a way to find identical files in two torrents, and link them - so they combine the pools of both and seed to both for where those files are concerned. In fact, my only issue so far is that on my stop+copy+recheck+start method, is that if a file, like a text file is added to one torrent, the size becomes different, and thus because the part size discrepancy, not all 100% of the finished is there, and it removes the parts that don't match for size. Such a feature may still even save the working parts as unfinished pieces for the other torrent with different part size. I think such a feature would make all of this easier, and be helpful for people like me. Who often go for hard to find items and torrents, and come into situations like this often. Like when I found a certain torrent in the past, by searching for the individual files, I came across another not-so seeded torrent, but got exactly what I needed fortuitously.
Could this be added?
Well, as for 'swarm merging', I think it should be added :)
One can sort of accomplish a similar result as mentioned above without it, but it is far more of a hassle.