That depends on how powerful the hardware is for Nintendo's next console/handheld is. I'm certain Nintendo will have something strong enough by then. The New 3DS probably could of run the Ice Climbers.
That's not the point. Think about it like this...
Let's say every character costs units to function. Mario costs 95. Link, 100. Rosalina, 110, and Olimar 120. So in Smash 4 they take the most costly character and then multiply it's cost by 4, which'll determine the amount of space they can use for stages, items, AI players, online modes, and so on. 4 Olimars costs 480 units. Now if they wanted more items on-screen they could cut the most costly character down or just remove them... But then 4 Rosas comes out to 440. That's not really a gigantic reduction. Cut her down and then you can get to 400. Past that it's not really reasonable to reduce the amount of units a character takes.
Ice Climbers... Take a guess what they'd come out to. 200, minimum. Probably more like 250 or even 300. 200 x 4 is 800 units, though. That's still a ridiculous amount more then the next most costly character. Besides transformations (which I don't think will ever happen again) I can't think of a character that'd take up anywhere near that much power. A proper Inkling might be 150... Cut one obscure character and you get that much more room for the rest of the game, and anybody not playing the ICs gets a more optimized game.
Even if they could get the ICs functional on the next handheld, they could instead allow up to six players and limit it to certain stages and cut back on items like on SSBU. If you have enough for ICs and six players they'd probably bump it up to eight, or maybe ten if they were crazy. Either that or 100% game parity (not necessarily graphics, but at a respectable level) with the console version. And that's with my lowball estimate.
If anything the ICs came about from the failed eight-player smash from Melee and they wanted something to use up the space. Now that eight players is a reality, they can't allocate the space for the ICs.