-Interchangeable UI. - The ASCII version UI is fairly confusing to look at and would be made much simpler with a setting to flip between the modern and the ASCII version UI while keeping the game visuals the same.
sadly, due to the update philosophy the old style ascii U.I. will not be making a return. The new interface is *personally* unenjoyable for a number of reasons, so I agree with your interest.
one thing you should keep an eye on is the DFhack project. A recent poll went through and prioritized an update to the DFhack "manipulator", which was a super well designed and handy tool for designating tasks and labors. Hopefully with enough time and support the community can return the ASCII mode to a playable state
ASCII is much superior to tilsets as you are not forced into perceiving items according to the arbitrary representations of an artist. symbolism baby :]
However, a number of your concerns can be addressed immediately:
1.
Color scheme works in the same way as before! At least for ASCII. be aware I had some issues with certain tileset sizes when installing them so finagling may be required
2.
Liquid Depth is a button nearby the minimap in the upright corner of the new U.I. No, it is not your fault you missed it - the new U.I. has issues differentiating between buttons and displays
so, with a little patience, we can hopefully return to the golden days of ASCII beauty.