Probably a few years away if the time it took for rural Band 28 4G to become a thing here is any indication. To be honest I can't really see the networks investing a lot into rural 5G coverage where 4G isn't even close to exhausting capacity. They'll probably add capacity to 4G (by adding additional higher band carriers e.g. 1800/2100/2300/2600 to take on demand nearer the tower) before they consider 5G deployments. Only rural 5G deployments I foresee in the next few years will be town centre sites and possibly COW sites for big events. Happy to be proved wrong but just going by what has happened in the past this seems the most likely scenario.