Aside from the obvious difference in reaction spells and abilities, there isn't any other conflict. I can give you the exact same argument.
1) Stunning Strike - The end of your next turn
I run it same thing as Shield. Aside from the AoO scenario there isn't any other conflict.
2) Shield/Absorb Elements/Dodge - Until the start of your next turn
Already discussed
3) Reactions returning - At the start of your next turn
Already discussed
4) Help/Ready - Before the start of your next turn
No conflict at all because they are actions.
5) Ongoing spell saving throws - The beginning or end of a turn, determined by the spell
All these are at the start/end of each of turns. Not next turn, so no conflict at all.
6) Surprise - until the end of your first turn
Why not "next turn" then if we can equate first with next? My reading has no conflict with surprise.
7) Assassinate - Against creatures who haven't taken a turn
No conflict
8) Dash - for the current turn
No conflict
In any case, it seems like the majority think that my reading is bizarre, so I will try to use your reading in other discussions. As I said I have no problem with either reading because it's not that important. Out of curiosity I asked my gf to read the rule and she agreed with me so at least I know I'm not completely crazy. Or we could both be crazy, dunno. I'm not changing my mind anyway :p
About the coupons:
If you get a coupon from an outside source, yes, the next visit will be the first. If the store is the only establishment that provides the coupons through the first purchase, then you need to make your first visit, get a coupon with your receipt, and use it on your next. Let's not compare apples and oranges here. The definition of next is the same in every language. It's the exact same language used in my country too. Buy something, get a bonus/points/discount for your next purchase. If you have already have a coupon from another store/magazine/whatever or someone gave you points etc, then you don't need to have your "first" visit, your next is your first.