There’s some obvious problems with it, as it’s implemented on the iPad, scaled down to the phone.
The average iPad (lets define “average” as a 9.7 for the sake of argument) is more often than not used in landscape, and still significantly bigger than the average iphone (lets say the standard 6/6s/7) size. Even more so because that standard phone is only used in the home screen in portrait (landscape home screen is only available on plus size). That is to say, there really isn’t much more to include more icons of tappable size on it. First potential benefit down.
Then there’s the multitasking aspect of it. 1) It’s not implemented on phones 2) The spaces concept would be difficult to use on phone if it were. Strike 2
Finally, the gesture itself. Short swipe up brings up the dock while long swipe up from the bottom enters multitasking on iPad. There’s enough room for control centre and multitasking there. Doesn’t make sense on the phone. I guess it could be short for Dock and long for CC but again, not much utility with only 4 icons and no space for Handoff/Recent/Suggested icons. Strike 3 I think.
What I’m getting at is, I can’t really see the point. It could look more like the iPad dock on the home screen but that’s probably about it. I’d quit like that. I can’t really vote for your options though.