Overall, a central API might be quite good, as long as it still lets other APIs adapt to Minecraft.
Thing is, one of the greatest strenghts of forge actually is the fact that it is highly adaptable and evolves quickly. As Greed already mentioned, this one will be really static, so only one party, the modders, is felxible and needs to adapt, possibly making it a pain to implement new mechanics and such, since the API has no direct nodes for this and the modder needs to code an adaption to another node, making it more resourcedemanding and most of the time slightly buggy. Also, this API will be only slightly faster to be ready than forge is, since the work to code it just hops from team Forge to team Mojang, meaning they have more work to do and need more time, resulting in a later release of minecraft overall. Also, if there is a problem with Forge, they can react quickly and tweak it, in this time you may even use previous versions, and having a solutuon in minutes to days, whereas you would have to wait till the next version of Minecraft when using the central one.
TL: DR version: I am really sceptical about a centralized API.
Thing is, one of the greatest strenghts of forge actually is the fact that it is highly adaptable and evolves quickly. As Greed already mentioned, this one will be really static, so only one party, the modders, is felxible and needs to adapt, possibly making it a pain to implement new mechanics and such, since the API has no direct nodes for this and the modder needs to code an adaption to another node, making it more resourcedemanding and most of the time slightly buggy. Also, this API will be only slightly faster to be ready than forge is, since the work to code it just hops from team Forge to team Mojang, meaning they have more work to do and need more time, resulting in a later release of minecraft overall. Also, if there is a problem with Forge, they can react quickly and tweak it, in this time you may even use previous versions, and having a solutuon in minutes to days, whereas you would have to wait till the next version of Minecraft when using the central one.
TL: DR version: I am really sceptical about a centralized API.