At this rate it seems that with Marvel not doing that great in the box office and with critics, it seems that Disney wants to prioritize Avatar over the Avengers E ticket for the next big thing at DLR post Tiana's. Plus with fans and even the studio themselves not to sure about the overall direction of the MCU coupled with the fact the franchise could be undergoing a reboot post Secret Wars, further explains why there has been no movement on this ride. Why commit to an attraction that could have elements in it that could become outdated quickly even more so if the franchise is rebooted post SW.
For an Avengers E ticket, I think the way they should go about it would be to wait for the series to be rebooted post Secret Wars. Keep the Multiverse or something like it as the underlying concept that would allow for a catch all team up attraction as well as the IOA Spiderman/Transformers SCOOP ride vehicle. Then craft a storyline that would allow them to swap out the main villain as the MCU or whatever the rebooted universe is called evolves. And to make this more interesting, have multiple villains the heroes have to fight like IOA's Spiderman. This would also be a perfect application for Disney to use those black box/digital effects reset patents.