If they did 747SP they could as well do the 747-100 & 200 and 300 as they all have more or less same cockpit layout & systems.

Proper 747 classic series, that would be just awesome... I'm sure it would sell very well, just think all the different versions CS could do and sell in separate expansions:

747-100/200 base pack

747-300 expansion pack

747SP expansion pack

747 classic cargo / combi expansion pack

:D

To me it definitely looks like the best option demand wise.