I prefer the modular approach. USB is an old technology which could go out of favour in the future, or drastically change. Same with onboard NIC's. To future proof the machine, I really do believe that the modular approach is the right one. I understand your point of view though.
USB:
Well, I don't see USB going anywhere soon, and given the scope of the machine being classic in nature and its slow bus speeds (talking about all future bus speeds in comparison to modern tech.), having the ability to plug in a DVD/CD drive is an important basic feature, much like having a floppy drive capability for those who need/want to continue using them. Parallel and Serial ports of old can be utilized through USB (with drivers) at a far cheaper cost (an adapter) than buying a module for USB. Just look at the current cost of existing module.
NIC:
The easiest way to update the computer would be to have access to a network/internet in a cost effective manner.
I understand your point, but by that way of thinking, to keep the computer at pace with the world, all devices on board should be modules. Thus the form factor should be like a larger, more modern modular system. (Big RPi or A4K replacement) But the form factor has been chosen by the developer to be for the A500 & A1200 without having to cut or modify the case so where do all these add on cards going to go/come out of the system? The number of outlets for expandability are limited by each case in question.
Price will determine the success.

And yes, I am smiling . . . :lol: