What is still the single biggest headache when you translate with GPT, DeepL or Google?

If you use DeepL – what would you need to finally pay for GPT translation?

Which features are still missing in current classical or LLM based translators.

How do you prefer pricing: SaaS, per-token, seats, or a flat plan?

Context: I’m exploring a side-project and don’t want to build the wrong thing. Not looking for promotion—just war-stories and must-have features (LLM model selection? scanned-PDF OCR? bilingual output? segment-level edits? glossary? missing format support?).