I recently talked with two people from Hacker exactly about this topic.
The TD series is indeed discontinued and the EL series will be continued. I was told that the decision was definitely not made because of quality problems but there seem to be major problems with the supplier in terms of communication and trustful business relationship.
So it is up to you to either buy some of the last TD servos at massively reduced price or to go with the EL series with a reduced featureset but still a very good servo in my opinion.
I don't have any information about a possible development of a successor for the TD series but I'm quite sure that there is something ongoing behind the scenes. But as I said, no real information or confirmed timeline about that.