I'd like to see them go in a dramatic new direction in setting or tone, even mechanics. Dying Light has taken ownership of the dramatic, modern-day limb chopper, Dead Rising (while MIA) kinda cornered the wacky market.
I liked Dying Light but actually preferred Riptide more.
Possibly because a lot of the experience was had before playing Dying Light but there was something great about the jankiness and setting.
I love open world games too but felt these games worked better being more closed off. From memory the weapon crafting was a bit better in Dead Island and there was a better horror feeling and sound effects.
We know absolutely nothing about what kind of game Dead Island 2 will be. However, Dying Light has drifted away from the zombie focused formula, so if Dead Island 2 is a zombie gsme, they won't be directly competing. Probably.
Based on dev schedules, I'm expecting the new version of Dead Island 2 to be announced this year.