As I've read,
Next reply sequel will be 1974, so far this is the speculation. However there are some rumours that it could be 2002 (it seems that's what the fans prefer).

Source: 
Korean



Which one do you foreign fans prefer? I'm not a follower just curious.

2002 was when Korea won the World Cup, wasn't it? That would be interesting. I also think the '70's would be cool too.

I'd love 2002. All I really know about 74-75 is the political atmosphere and I don't really know how well even that would lend to a series like this. 2002 allows for a much different demographic too, which would be nice.

I'll go for 2002. That's totally my high school era!!!! Hahaha... >_<

Oh I thought they won it. Haha! I just remember everyone was going crazy then and going Go Reds! I used to play dress up games online back then and I totally remember the the Candybar dolls dress up games had all the Team Korea Reds outfits and I was like what is all of this? :p Btw, if you don't know what Candybar doll is I have one on my profile. (*^_^*)

I'd be happy with them going either way as I just really enjoy this series. It'd be nice if they could tie whichever one into one of the other ones somehow, sort of like the 1997 crew popped up in the 1994 series.

I was hoping Reply 1981 or 1982...so much. The next best would be late 70s. 2002 is WAY too recent.

What nostalgia is there in 2002. Aish! That's partly what made 1988 so special!! Those who are younger, you will be privy of a glimpse into a time you never got to see. Enjoy the experience. In 10 years they can do 2002.