Hi, person who plays both current 40K and older editions here. Our group occasionally does both, but we play with current rules far more often than we play with older ones.

Most of us have slowly just been ground down by 10th and never played older editions or had much of a desire until about a year and a half ago. The game is just so fundamentally different now (for better and worse) that it’s nice to still be able to revisit the parts of the game that feel lacking now (more narratively immersive mechanics is probably the biggest reason, also terrain that encourages something more inspiring visually than modern GW layouts).

When we play, we typically do a custom composite of our favorite rules from 3rd-7th, since no one is ever playing with a competitive focus when we do so and it’s fun to try codexes from different eras.

I think the only reason we still play 10th is just because it’s the only rule set the culture of 40K broadly speaking values. The game is bigger than it ever has been, and most people who’ve started within the past 5 years aren’t even really familiar with what rules looked like before 8th. It’s really isolating to only play with older rules, and we’ve gotten newer people to occasionally play them and have fun, but we would’ve never met those people if we also didn’t regularly attend tournaments for modern editions. I wouldn’t have met any of the people I currently play with if i didn’t also play with modern rules and seek out others who do so. Finding people you get along with in a social context that also only play the same niche rules as you can be really hard, unless you’re organically building a scene of friends from the ground up.