Very good question. I wouldn't mind for Winter Memories to make me winning over the heroines again, as in a new timeline way rather than a continuation. But the Alpha suggested it to be a hard sequal to the harem ending in Summer Memories and therefore no old savefile is needed nor any other data. Standalone.
I wonder if we already know how many days it will take place. The Alphademo thing showed us that time passes differently from Summer Memories, slower, at a hour-to-hour basis the characters change location instead in the old game, skipping to a new time-of-day zone. Which means that a day must feel much longer in Winter Memories than in Summer Memories, I think.
I did like the aspect of slowly winning over the heroines, but I can bare with it following the timeline.
1. Though I think if he implemented a memory mechanic where certain actions will jog their memory of the last summer would be neat.
2. Or you start off with one of the girls of your choosing as the heroine that remembers the last game. And once you win over another heroine you'd get words like
"Why didn't I do this with aunt Miyuki last summer" or
"I wish I met Boku earlier, I want more memories with him".
Akari? Boku was too timid to talk to the menko kids.
Heck for Kagami it can just be explained you never went to the school, and for Shizuku you just never noticed she was the chick on Dwitter. You can come up with something for the other girls.
(Dojin Otome is already in finalization stage so anything more will probably make him burnt out, or unless we ask for a optional DLC that adds it. Sadly we mostly likely aint gettin it)