It bothers me that imports of UK OS OpenData into WGS84 might mean that each year those points drift out of sync of real locations by 2.5 cm north-eastwards. Not only that but the further back in time the further out OSM data could be. I don't know if this has been considered or corrected for. Additionally OSM has no true way of knowing the WGS84 epoch of a co-ordinate, for the uploaded API changes occur at some arbitrary point in the future after survey. The uploaded GPX traces can be without timestamps and thus unknown drift also. Ordnance Survey use ETRS89 and ETRF89 datums to correct for plate tectonic movement. Is that what happens to UK co-ordinates stored by OSM?