I like the idea. This, maybe combined with a slight buff to hand cannoneers (lengthly discussion here: Hand Cannoneers bad state confirmed), would benefit Portuguese, Spanish and Turks without changing the general character of those civs.
It also addressess the often heard complaint that Turks have no viable trash units.
The only risk is that it adds too much for Spanish, which is already an average civ and strong on closed maps like BF.