Algorithms may be awesome, with a lousy (non-familiar) presentation (not enough UX design), no impact whatsoever.
The security distributed search engines would need to offer can be framed in terms of confidentiality, integrity and availability. The most probable security threats are information leakage, integrity violation, denial of service, and illegitimate use.
Gateways and internet facing demo search engines are not part of the dweb infrastructure, nor are they essential, but they are important for the transition to dweb. Running an internet facing gateway or search engine means using serious hosting that investigates and forwards abuse emails so cases can be investigated and responded to instead of being null-routed immediately.