Yea, for SATA ports, I used to use a board with six of these, and I ran out. Now i have one with 8, and have all of them in use, and use a RAID controller for extra. I don't think 10 is too many, but anything more than that is really pushing it, because you start to get to the point that you will have trouble fitting enough drives in a standard PC case to plug into them.
I disagree for the USB ports a little bit. I definitely wouldn't want to use an external hub if I can avoid it. Happy to use the ones that go on the front of the PC case though. 6 USB 3.0 slots is probably plenty for most users, as it seems unlikely to me that users would use more than 6 USB 3.0 capable devices at a time. The only reason I think that OEMs shouldn't bother with more, is in situations like this where it starts sucking HSIO lanes away from other potential devices, in which case it would be much better to implement USB 2.0 pots instead. If that wasn't an issue, I'd say you can't have too many.
M.2 devices, I completely agree here. I honestly don't see the need to have more than two of these, especially given their cost at the moment. Although, later down the road when they are as cheap as HDDs I'd rather see nothing but these (though, possibly connected via some type of cable to conserve space on the motherboard) but that is a long ways off.
Ditto Someone Somewhere on the LAN and video ports.
It would be a lot of fun to design your own board. I've wanted to do that for a long time now. I'm a big fan of integrated hardware, so I'd love to see more robust integrated audio and other devices, so I definitely agree with you on that one. Although I don't agree with all of your points Nyhil116, I'm glad you posted them because it is important to see what others like in a product. It is fortunate the market is usually overfilled with motherboards to give us a lot of options, because it is rare that a board has everything that everyone wants, but may have everything someone wants. In this case, the board seems overloaded with parts, but it's trying to draw in everyone even if it drives cost up at the same time.