I am just a dumb customer of AA and don't have any inside knowledge, but I have had a linked e-ticket issued (with more than 16 segments), so the capability is in Sabre today. Whether there are other problems (maybe in back office processing) making this undesirable is another question; certainly AA seems to try hard to avoid using this capability and most AAgents are clueless about it. It worked flawlessly for me so it would seem to be a viable and working feature.