One assistive technology that is used to help students who are deaf is FM systems. With an FM system, a teacher just talks into a microphone and the FM signals transmit the teachers words at a constant level. According to Gallaudet University, there are two different types of FM systems. The two different types of FM systems are personal and sound field. A personal FM system is paired directly with an individuals hearing device whereas the sound field is an increase in sound to a group of people. You can get more info from Gallaudet University here https://www.gallaudet.edu/clerc-center/info-to-go/assistive-technology/assistive-technologies.html
As for the future of FM systems, I believe the direction they will go is improving the quality of the device and also making it more available for people to use outside of the classroom. I believe that this device will improve in the future by increasing the 50-165 foot range to a distance that is much greater. Overall, I just think the future of this assistive technology is just in the improvement of what is already here.
Sources
http://www.lifeprint.com/asl101/topics/public-education-for-deaf-and-hard-of-hearing-students.htm
https://www.gallaudet.edu/clerc-center/info-to-go/assistive-technology/assistive-technologies.html
https://www.hearinglink.org/living/loops-equipment/fm-systems/what-are-fm-systems/