Well, if you really want something to make, I would like to have a module for firing "energy bomb" ammo, like a bomber or siege starship's shots, and I don't think any of the existing turret graphics cover the "big slow-firing single-shot cannon" role
Only if you're really looking for something to work on like that
Railgun and Railcannon modules also sound interesting; I could use the existing sniper turret for that, though it actually looks like a 3-way gun (iirc).
In any event, many thanks for the offer of assistance