• Significant technical concern with the viability of the work
• Significant procedural concern with the ability to complete the work effectively due to low energy levels, contentiousness, etc.
• Lack of technical clarity on what the work and deliverables will actually consist of
• Lack of scope for what is clearly in-bounds versus things that should be explicitly forbidden
• Overlap or interference with other work inside or outside the IETF, which would lead to clear harm or significant operational issues
• Quality of writing and editing poor enough to prevent effective external review of the proposed work
• It's a really really bad idea (e.g. key escrow)