I'm pushing for the hash-based solution because it can be implemented and developed quickly and easily and fixes the main issues we've seen on testnet:
- routing sync on mobile nodes
- "route not found" errors when you're missing routing info.
It can be deployed as an optional feature and will give us time to specify and implement proper IBLT-based filters. It can be combined with the timestamp approach: nodes would send bucket hashes + low and high watermarks.