Before we go here, what is the alternative. If restrict soda and people switch to beer even if they will be driving that could be much worse. (I don't otherwise know how the effects of alcohol vs soda come up but that too is a question worth asking)
If I recall correctly part of the origin of soda was doing the reverse, from efforts to actively substitute for alcohol. Hence why they emphasized as "soft drinks" as a marketing category.
As for other substitutes, we've seen highly sweetened coffee drinks as the common one, to the point where soda taxes started to face accusations that they are actually thinly veiled classism due to exclusion of more white collar "Starbucks" type drinks. Rightfully or wrongly they have a point about it at least looking bad.
I wasn't intending to imply that is what would happen. That is the worst substitute I can think of. If high sugar coffee would also be counted as soda for the laws - something that isn't a given - this seems even more likely.
I don't think that's a relevant comparison. They're both beverages, sure, but that's about where the similarities end. As drugs they're entirely different. May as well add Ayahuasca to consideration as well.
I could see tea or coffee (particularly the sweetened varieties) and sparkling water, but honestly I think the most likely alternative will just be plain ol' water.
