I’ve had this same thought, and I’m surprised nobody has experimented with this yet.
I’ve only tried one D-bearing yoyo, and it’s probably my 3rd or 4th favorite I’ve ever thrown. It was also Titanium, so it’s hard to say how much of that was due to the bearing. Imo, centering C or D bearings are fine. What I haven’t liked in my experience with them are A bearings. I know there’s a cult following for the MR85, so maybe I should try one of those sometime.
There are some YoYo’s the Hubless did it. Bigger axle diameter means lower rpm means slower feeling YoYo. Could be fun in responsive play but would need getting used to in unresponsive and massively increase the thunk feeling at the end of the string
Honestly I vote for this 
The M bearing in the second version of the YYJ Big Yo was 9 x 17 x 5 mm.
The old Metric IlYY Large Bearing (6x13x5 mm)
i prefer whatever size bearing the yoyo was designed for
Rei is the real G.O.A.T.
D bearing is my preference for the reasons already listed. It’s why I designed The Gnome using one, and my sig The Talent also features one!
I will offer a difference of Opinion.
In the Organic Shape realm…
Responsive = MR85
Unresponsive = C (Note- this makes it easier for me to half spec and make it responsive)
When is that coming out, btw?
June 21 at the Mile High Jamboree and I will have them the next weekend at Nats. Available direct after June 21 if you can’t catch me in person.
Size E
Or
Size I
Can we get a peak at how this looks?
Edit: Sorry send me a peek?
Please keep this post the bearing chats 
For unresponsive, I’m really enjoying D Bearings, I only have a couple, but the play and spin time is awesome, gentle throws generate a ton of power
That said, I’m partial to C as well because the parts are easy to get and are plentiful. D bearing pads seem like a pain to get in my limited amount of searching
For responsive it’s hard to pick, design in that world is all over the place, and it’s the complete picture that matters, no just the bearing
