Just a thought that seems to be a logical and responsable step for Google/YouTube.
Allow viewers to rate videos (and advertisement, comments, etc) into categories similar to the MPAA rating system (or the like). Also implement a filter based on these public ratings so that one can browse YouTube in a "kid friendly mode" for example. This would allow me to show my 7 year old a silly lego animation without the barrage of adds and follow up videos that are... well, clearly not kid friendly.
The current safety mode is a good start, but it is clearly not enough.