First of all, I want to thank James for being a champion of a great product line whose value proposition just kicks every competition's behind. I own an X5 and used to own an X3 and various versions of E12, and have been one happy customer over the past couple of years.
1) One thing I would really like is just a better way to search albums/songs...Just got a Sony NW-A17, and although I prefer the X5 sound, I end up using the Sony more often in portable setups, simply because I can get to songs and albums faster. I also have a Sony ZX-1, but I actually prefer carrying around A17 for the same reason. ZX-1 has an android-based UI, but it still makes you scroll quite a bit through its GUI, whereas A17's non-android UI, while with its shortcomings, allows me to jump to different folders alphabetically (See attached photo) with just front buttons. It really is a huge difference especially if you are talking about large storage space. My X5 is fully decked with 250 Gbs worth of songs, and the current UI simply makes it a hassle to access, say, any artist that start with an H, for example... I know X7 will be Android-based, but having either a search function within the player app or ability to jump to different folders as seen in A17 would be very, very helpful.
2) I think if you can include RSA-4pin LO in addition to HO - not so sure how realistic this would be - so that I can better appreciate my old RSA SR-71B or CLA Duet, that would be a huge uptick in my book, although I realize that there would be many who could care less about this feature.
3) Finally, I want to see an optical out over the coaxial seen in previous Fiio DAPs. I understand an optical out would likely have jitter issues and so on, but there aren't many portable DAC/Amps with coaxial input, so I think it makes sense to have an optical out. I have always been a fan of HiFi-M8 and Theorem - in demo rooms only - but never made the plunge because my X5 only had an coaxial out. Actually, I guess James helped me save a few bucks...
All said and done, I will still go out and get an X7 when it comes to the market even if it doesn't have all the features I want because I know it will be a great sounding player given James' track record. Keep up the good work!