User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-34104032-20171228202853/@comment-34104032-20171230133938

Can't provide that info, I only use google translate and bing on the chinese translation and so far I have not found DX4 but most likely the answer is not there (probably in vol 25).

I only said AxA should be his next power (Ise mentions it) and probably the last power up he gets, and based on the info till now DxD and ExE will be equal so it can't be considered as a power up but only as an improvement of DxD (in EX Ise says the dragon form is more fitted for powerful large-scale techniques); DxD is dragon god class in small packaging and ExE is dragon god class in big packaging.

Some spoilers (seem to be accurate) for vol 24 can be found here:

https://tieba.baidu.com/p/5438014483