Huh. Somehow this slipped through. Apologies for not responding before.
The anthology will consist of 10-12 stories, with a total length of 60K words. Therefore word count for each story should be 1K-10K, with the bulk around 3K-6K. Longer or shorter than the 1-10K range are possible, but will face a higher bar.
Topics: The book is to raise money for the Ukraine Appeal, so ideally, would reference the war in Ukraine and what things might be like 10 years on. There are many possible takes on that, and I won't turn away out of hand those stories that are somewhat tangential, if the theme is good enough.
As for theme, I'm hoping to have a largely upbeat book. Stories about how everything is going to go to Hell, and the situation is doomed isn't going to encourage people to contribute to reconstruction. That said, there will be space for downbeat visions of such come along.
I'm not particularly interested in "war porn", with detailed descriptions of the damage high explosive and flying metal can do to human flesh. Trinketisation - where the story is about the neat Weapons of War with the humans involved being a secondary concern is also going to have to be of a high quality. If the anthology looks at different futures, be it at high-level politics or a simple description of dealing with the large number of people with PTSD that will be around, or an ongoing frozen conflict, or whatever your imaginations can come up with.
As an Editor, I judge a story on three interwoven categories.
1. Characters. Interesting people that emotionally affect me. I don't need to like them, but I want the anthology to look at the people involved.
2. Plot. A story is about interesting things happening. There may or may not be a resolution, but if nothing much happens in the story, it's not going to hold the attention of the reader.
3. Setting. It might be Ukraine as we know it. It might not be. But the stage of the story needs to be convincing.
That's all. Interesting people doing interesting things in interesting places. If you get all three done brilliantly, you're a better writer than I am.