Moving towards less disposable products is good, obviously, but damn I would be annoyed if I was in that Paris marathon targeting a PB and got slowed down by having to wait to fill up.

Mandatory refillable bottles are now ubiquitous in trail running, and I think that's fantastic. It's an environment where targeting specific times makes less sense anyway. But for road races, I think Paris's idea of making it mandatory for anyone slower than 2:50 is too extreme. I would be much more amenable to it if the cutoff was 4:00. I feel like that's roughly the slowest time where people are seriously targeting a specific time, rather than their goal being just to finish.

Chicago's optional refill stations will be interesting to watch, but seem ultimately pointless. I doubt they'll see much use.

I'd be willing to bet that a much smaller number of runners will use them if the pre-filled cups are still available. Sounds like there are some lessons to learn from Paris, but only offering re-fills is doable. There are plenty of trail running races that make it work.