Keep in mind your instance will cache thumbnails of remote content… including possibly illegal content for your area.
For example there’s (far too) many instances that host or are themed around “lolicon” - which is cartoon child pornography. That’s illegal in some jurisdictions.
Also remember federation is a two way street. The people you’re going to attract with this concept are largely the same groups many instances are trying to keep out. If you get even a little popularity I would expect many mainstream instances to defederate you. Then you’re basically back where you started - what’s the point?