TL;DRIn order to solve the bots versus belts issue described in Factorio Friday Facts #224, bots should be nerfed with additional maintenance costs.
What ?The batteries of bots must be exchanged regularily, so that the use of logistic bots costs batteries as maintenance. These maintenance costs should be made so high that the effective transport costs of every item transported by a logistic bot is, on average, one iron plate.
Why ?Factorio Friday Facts #224 and its accompanying 44-page (!) discussion thread show that, in the late-game, bots are clearly overpowered compared to belts and must be nerfed in some way. However, they should not be nerfed so much that they are no longer useful.
Nerfing by increasing the power requirement of bots would not solve the problem, because the player could just build more solar panels. Also, nerfing by increasing the production costs of bots would not solve the problem, because it would just take longer for the player to reach the desired amount of bots. Therefore, in my opinion, the best solution to the problem would be to introduce an additional maintenance cost, so that the more the player uses bots, the higher the resource cost to the player.
This maintenance cost must be more than just "free" electrical power, it must cost actual resources, so that the costs can actually hurt the player if ignored. Therefore, I am suggesting that bots should require batteries not only when building them, but also in order to maintain them. This would also be realistic, because in real-life, even rechargable batteries must be exchanged from time to time.
If the transportation of an item by logistic bots costs, on average, one iron plate, then most players would not want to transport large amounts of iron or copper plates with bots, because the transportation costs would be just as high as the value of the transported item, which would effectivly double the production costs.
However, for transporting small amounts of items, such as expensive end-products which already required 200 iron/copper plates to produce, nobody will not care if the transportation of the item will cost an additional iron plate, since that would only be an insignificant price increase. Most players will prefer to pay this slight price increase, if it saves them the space requirement of an additional belt going through half their base.
That way, bots would no longer be overpowered, but still very useful. Most megabases would use belts for transporting large amounts of items (especially ore, plates, green circuits, barrels) and would use bots for transporting small amounts of expensive end-products, such as science packs, destroyer capsules, and possibly also blue ciruits.
An additional reason why most players will not want to unnecessarily use bots anymore instead of belts, is that, the more they use bots, the more battery producing industry they will have to build to maintain these bots.
However, one disadvantage of this suggestion is that delivering iron plates to the player by bots would effectively make these iron plates double as expensive. Therefore, the player will not be able to afford this luxury in the early stages of the game (which would not matter much if logistic bots are only unlocked in the later stages of the game).