From my knowledge of the BRouter codebase and past contributions, it should not be a big deal to move from 5x5 to something more web tractable (as 1x1 latitude/longitude).
Armchair only, sorry. Closest thing I've come to regarding brouter sources was wondering about what it would take to add relation names (road names). Because that could not only help route consumption (better turn instructions), it would also enable adding "road change" penalty to the rules: currently that's only based on direction change, which causes trouble in mountain environments where steep straight connections exist: the turn penalty affects the gentle switchback climb/descent harder than the undesirable straight.
BRouter works by relying on segments (relevant extracts from the OSM data, in a custom format) of 5x5 latitude/longitude degrees. See https://github.com/abrensch/brouter/blob/f3895791766dfcd7cd0... for their creation (full doc https://github.com/abrensch/brouter/blob/1765ec45230e337319c...).
From my knowledge of the BRouter codebase and past contributions, it should not be a big deal to move from 5x5 to something more web tractable (as 1x1 latitude/longitude).