I'll add more as you guys make suggestions & add them here for everyone to see.
Galactic Geek:
1) More accurate frame data.
2) damage in frame data shows damage per hit + total damage for basic combos & other multiple-hitting attacks.
3) Have access to normal attacks, basic combos, & special move variants in counter-attack section under AI options.
4) Ability to switch stages mid or post-match (could even be used in main game along with character selection option).
6) Ability to switch position of characters on the fly to stand in front of interactables, similar to the left & rights sides of the stage.
RedRaptor10:
7) More robust, detailed, & interactive tutorial mode.
8) Audio cues for learning combo-timing.
trevor91:
9) Player-based AI (similar to Forza Motorsport 5's Drivatars).
RYX:
10) Less lag during online practice mode.
Rathalos:
11) Ability to save settings upon exit so they can auto-start upon next visit to practice mode.
Red Reaper &
K.O.E_18:
12) More robust recording mode.
Galactic Geek:
13) Allow for more than 6 tagged moves.
14) Allow for tagging of moves in online practice for both players to see & use.
OmegaK:
15) Hitbox/hurtbox data (e.g., visual representation).
16) Audio/visual cues for punishment windows and blockstun.
DarkPage:
17) Allow online practice mode for only 1 player.
18) Then allow for online players to "join" online practice mode mid-session (with open, friends only, & invite only settings).
19) Have game-speed adjustment settings that mirrors various kinds of online lag.
Eddy Wang:
20) Have setup slots in record mode that can be played back-to-back at different frequencies, even randomly.