Personally I liked the non-restrictive elements of Pikmin 2 much more than the limited and timed day mechanics of the first Pikmin, so if the timer returns (which has strongly been hinted at) I'll be a bit disappointed.
I don't see Olimar's recovery being changed exactly, I mostly imagine the Pink Pikmin, depending on how many you currently have, will sort of pull the Pikmin chain up a little, raising Olimar a bit. The amount of Pink Pikmin will obviously affect how good the recovery is, with none it would be like Olimar's current recovery, and with multiple ones it would give him quite the boost upward (and probably diagonally in the direction the chain is facing). At least, that's what I predict will happen, the tether aspect I don't see going tbh. Rock Pikmin I guess would be like stronger Purple Pikmin, but maybe they'd be rarer, and weigh down the Pikmin chain a bit to make up for the Pink Pikmin.
As for Luigi, I'd honestly prefer they change Mario's FLUDD (maybe make it something Galaxy-related, like the Luma spin thing). If he didn't get the Poltergust for Brawl, I'm not convinced he'll get it now, but it'd certainly be nice. Though I'd probably end up preferring his current down special more (assuming his down special is the one that implements the poltergust).