I'm actually making a mod, called WC4 (=P), and I created a poll to know what you, people, think of this feature :
It seems that I cannot create a poll because I must create it in 5 minutes :sIn wcIII, you could buy units/items or use any neutral buildings, but in my mod, players will need to "assimilate" the neutral buildings, let me explain, players can uses neutral building only if it's owned by him or one of his teammate, there is two solutions; the first one consists of slowly conquering neutral buildings by having no enemies nearby, or if your troops are two times bigger... The second options consist of spending gold to assimilate it directly, but it cost a large amounts of gold which increases as time passes by.
Vote here