TL;DR
The stacked belts should be their own set of belt, splitters and undergrounds, instead of depending on inserters.What ?
The belts shown in FFF 393 should be their own set of items, that are dedicated to the purpose, with all inserters that have a stack capacity greater than one able to place on them. This would make the poorly named bulk/stack inserter redundant.When transitioning from a stacked belt to a flat one, (or from a higher stack limit to a lower stack limited belt) the stacked one would back up and send smaller packets on down the belt.
Why ?
There are several issues with the currently shown idea:- It feels weird to get a massive improvement for belts without having to manufacture any new belts, but instead inserters. It feels like improving inserters, not belts. In case of miners, you may get the bonus entirely with research, without any new infrastructure being built, which feels just odd.
- The cost difference of stacked vs non stacked belts is now entirely constant as it depends only on inserters, with no scaling with distance. This entirely disincentivizes ever using flat belts again when enough room is available, contrary to belt tiers, where it is usually cheaper to lay down multiple belts when you have the space available. Broad belt arrays are cool, so lets leave in a reason to use them, and make the fancy new belts appropriately expensive (aka more than twice a regular belt of their speed would cost). This would also allow for some optimizations of taking flat belts and re-stacking them into a stacked one, instead of just always using stacked ones.
- While factorio isn't strictly logical, it is very strange why inserters can move stacks between chests, assemblers, trains and belts, unloading in one go, except in the very specific instance of the belt, which now suddenly needs a special inserter to do the same trick that already works in every other case. This is quite hard to explain, and also confusing, since there are still quite some stack limits around. All inserters have them, not just the old stack inserters, and nobody will talk of a bulk limit. This can be all avoided by making it a property of a belt. You need a special belt to place a stack on it is very intuitive and does not need complicated word and name twisting.
- The graphics just don't look quite as good as flat belts, and surely could be improved by having entities that are designed for stacks. For example, in this clip the ore does not fit into the underground belt. By using dedicated graphics it would be possible to make the splitters a bit taller, add maybe some side supports on the belts to keep the stacks from falling. The undergrounds could also be made longer, even into 1x2 entities, to make them a more unique thing with its unique challenges.
- Such a massive upgrade applied to any and all belts without any possibility of differentiation allows for little granularity, and while it may just work for SE, mods would certainly love to get more control over belt stack limits than a flat one for any and all belts.