Better to change it for a much better move.
Smash 4's up-air had a lot of things that weren't good about the move, the only thing worse about this up-air is active frames.
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I think going over each move and applying thoughts and theories will be something nice to have. Let's see
Jab
Does the same job as in Smash 4, the IASA frames to continue the jab combo might be slightly faster than Smash 4.
Jab 1/2 don't pop people off the ground, possibly jab locks, even though jab locks are nerfed heavily, so we might be able to do jab 1 -> jab 1 -> d-tilt
D-Tilt
Move does slightly more damage than Smash 4, 10%, but still easily combos people into up-air and f-air.
Will be our best pop-up tool in vortexes if we catch people directional airdodging out of a throw combo or a low to the ground aerial chase.
F-Tilt
Move does much more damage, will be a viable kill move, and might be safer now. Tilts and jabs out of dash cancel is gonna be a very strong option, and this will be a scary high percent option off reads.
Up-Tilt
Hitbox was possibly moved so the hitbox behind Ike was removed, or the hitbox was just straight shrunk in size. FAF reduction is very nice, will make the move easier to use without getting punished. Will be used as a kill move or a custom combo finisher.
F-air
Regardless of how it looks in-game, move starts 1 frame earlier, but the hitbox reaching horizontal/downward might take slightly longer, it feels like some combos are harder because this move has an exaggerated animation in the beginning. If this isn't an issue, then the only issue will be using this move in neutral for spacing, since it doesn't autocancel.
B-Air
The landing lag change is huge. 9 frames is almost an autocancel in itself, just look at the Zero vs Leffen match on Skyworld, that was never an autocancel, that was the landing lag. It's almost un-noticable.
On another note, though, Ike's faster jumpsquat and jump velocity means rising back air is gonna be nigh impossible to hit on most characters, get used to falling back air, which is way better.
Up-Air
Get excited, it's that good personally.
Comes out slightly faster than Smash 4 up-air, will give us very easy throw combos, juggles and upward kills. Take everything Smash 4 up-air had problems with, reduce active frames, put it into one move, welcome to this up-air. We will catch air dodges, punish landing air dodges, combo heavily, juggle and vortex with this one move. It also kills if you catch people trying to get down or push a button in the air.
D-Air
Haven't seen much of this move, personally, it does similar damage to Smash 4 pre 1.2x damage multiplier, and likely still has the same Smash 4 spike hitbox...So yeah. Nothing to see here.
N-Air
It's lagless, it does less damage, it combos like Smash 4. Have fun. Oh, and it might have a bigger hitbox behind Ike, because that's nice.
F-Throw/B-Throw
Might do more KB than Smash 4 for stage control purposes like a lot of these type of throws, but no combos, we aren't Brawl yet guys.
Up-Throw
Juries out on combos, I see them in 1v1 1.2x multiplier matches, but some people say otherwise. I think combos are very consistent once you get past the super early percents, and at 0 you probably should just down throw. We probably won't have kill confirms off up throw, so get used to throwing off stage and pressuring edgeguards.
D-Throw
I wonder if it kills better than Smash 4. Excellent combo starter at low percents, but watch out for varying DI, they can go purely vertical, for up-air, back-air, n-air/f-air combos, or go really far away from you, where you'll need f-air to combo properly. If they can air dodge out, they'll eat lag, and if it's a directional air dodge, they'll eat another grab or a d-tilt for a return to the combo.
Smash attacks
Use them like Smash 4, they do slightly more damage, might have slightly less FAF...Pretty much Smash 4. D-Smash still pretty lacking.
Counter
Possibly 1.25x multiplier, kills on hard hitting moves like lightning kicks across stage at 40.
Aether
Doesn't go through stage anymore, if this stays our Mario MU gets really tricky if FLUDD is still good. Other than that, we might get around counters? Unlikely IMO, but possible.
Quickdraw
The FAF change means nothing, deadzones still exist on the move and it'll activate on air if someone gets even remotely close at a diagonal angle. Nothing much here.
Eruption
Move gains pillars by charging, 2 at partial charge, 3 at max. Will be an insane tool to edgeguard if ledge invincibility is nerfed as a whole, will be safer to use if you can get pillars out so you can stay away from the ledge itself.
Movement changes
Jabs and tilts out of a dash will make our dash in very strong, and will make our dash out almost like a psuedo perfect pivot back into jab/d-tilt, very good change for us that we'll need to learn to utilize heavily.
Remember, everything is subject to changing, we'll see what stays and what goes when the game comes out. 170 days till Smash Ultimate.