Make it possible to compose a graph view based on tags. E.g. to show all connections between notes that are tagged with #books . One possible implementation would be to highlight these notes and their respective inter-connections. This could be developed further into a query function. E.g. to highlight all notes and ther respective inter-connections that are tagged with #concept AND #political_science, etc.
Some implementations for graph views based on text recognition etc. were already being suggested. However, what made the RoamResearch buzz so big is that RoamResearch is customizable to everyones liking. Maybe Obsidian should go a similar way here and offer to show connections not based on opaque-algorithms, but instead based on the bi-directional links we already have, and, additionally, hashtags, which can everyone add in their own fashion. This goes in hand with the Obsidian-Philosophy of the markdown- and plug-in-based, DIY approach.