binary and qt together are mandatory for any coin
and instamining is relative, a big hash(renting hash) can "instamine" at diff 10 for example...
It is not really unfair people get something for what they can do rather than for how much do they have!
I don't know how could it prevent small miners, unless you are talking about the size of their brains.
No vendor-related binaries are mandatory. Only the sources are mandatory (unless you make a closed source coin).
The same no AMD or NVIDIA miner is mandatory, it is only expected by miners using this kind of stuff.