The possibilities are endless really. Could you list the forces/periods you already do?
Very true!

That's probably half my problem, but I've never bee quite this stumped before.
Core long-term projects I keep coming back to are:
- Maximillian Adventure in 28mm
- C16th Europe in 15mm
- By Fire and Sword (Eastern European Late C17th) in 15mm
So, not many - but that said:
Every time I've tried fantasy or sci-fi I've ended up selling them off and think I've finally learned my lesson.
Likewise ECW I have had and got rid of.
Likewise Mexican Revolution.
Likewise WW2 Early, Late, Russian Front, Poland.
Napoleonics I've never found a ruleset I can get on with, and likewise for C19th European Wars.
Spanish Civil War is a 'one day'. Russian Civil War I always wanted to do until I read 'The Bloody White Baron' and since then I've never had any desire to do RCW as a wargame.
Now it just sounds like I'm being picky!
Maybe linked to your C16th Ottomans, but a little different - how about the Great Siege of Malta in 1565? It's such an epic conflict.
Absolutely, this is one of my favourite epics of history, hands down. I'm just hoping Khurasan might release some figures suitable for the Knights of St John as all my C16th are Khurasan and they already have plenty of figures for other troop types, plus the opposition. So Malta 1565 is more a question of when, not if

Crusades I have sometimes considered - the advantage of later C14th though being I could do Free Companies, Chioggia, and the Alexandrian and Savoyard Crusades all from the same basis, so if I went medieval it would likely be later.
Sarissa have plenty of buildings to emulate a street in Germany if you so wished.
I hadn't seen those! Thanks. That brings something new to the equation, although you're right it's a lot of outlay for a relatively small game.