Improved ATC?

Would it be possible for ATC to instruct aircraft to slow down and speed up for approach around airports? This would make AI so much more realistic, and would make go-arounds rarer. It just seems so pointless that whenever I go to a large airport, about 5 aircraft try to land in one large 'cloud'. Could the speeds the aircraft is capable of be included in the aircraft .cfg?
Cheers,
Alex
Cheers,
Alex