Ok, there are two main trains here. You've got mod compatibility, which isn't something that Forge can control. You can't have forge require Tinker's stats for mod-materials without making Tinkers a part of Forge, which defeats the point. The same thing goes for he rest of the mods, the fact that they do things their way is what makes them separate entities.
The other thing is what should and should not be in Forge, and, realistically, what should be included in Forge is, in my opinion, the bare minimum. Ore and fluid registries were implemented because all mods were doing it themselves, and doing it differently, so unification of backend stuff was a good idea to clean things up.
NEI is troublesome for a few reasons, the first being that NEI itself already does the job quite well. Mods interface with that, rather than making their own system. How well they do the interface is a different matter. The other thing is that NEI does the job at the moment, but that's not always been the case. NEI took over from TMI (recipenook and a few others). Front-facing mods come along and replace others, because that's the way these things work.
If you add things into Forge, you disrupt that cycle.
Forge itself may also be replaced at some point, but that's a much bigger task.
The other thing is what should and should not be in Forge, and, realistically, what should be included in Forge is, in my opinion, the bare minimum. Ore and fluid registries were implemented because all mods were doing it themselves, and doing it differently, so unification of backend stuff was a good idea to clean things up.
NEI is troublesome for a few reasons, the first being that NEI itself already does the job quite well. Mods interface with that, rather than making their own system. How well they do the interface is a different matter. The other thing is that NEI does the job at the moment, but that's not always been the case. NEI took over from TMI (recipenook and a few others). Front-facing mods come along and replace others, because that's the way these things work.
If you add things into Forge, you disrupt that cycle.
Forge itself may also be replaced at some point, but that's a much bigger task.