Though they recently suggested it with a teaser site earlier this month (I'd link it but appears to have been taken down for now), Oreshika's remake has been confirmed by Sony - and it's for the PSP. This version will add new characters and scenarios, but also get a graphical improvement, an updated strategic battle system and the fields will see seasonal changes. Families can also create their own weapons as a memento to pass down through generations. There is also mention in this week's Famitsu of the ability to import save data from the PSone game, and some kind of ad-hoc feature that wasn't expanded upon.
Recently, game designer Shouji Masuda also talked about what direction to take the series in, which of course opens up the possibility of a sequel.
Ore no Shikabane wo Koete Yuke, which is being worked on by Alfa System (the developers of the PSone title), is currently 50% complete and does not yet have a Japanese release date.