I'll be surprised if they don't do this TBH. Think about it-
-By changing the old NSL signs to mean 50mph there's no replacement costs for new signs = no cost.
-Many drivers who don't hear about it, or forget, will get done for £60, x lots of drivers = extremely cost positive for government coffers.
-Government can trumpet 'increased road safety' due to all the motorists getting caught doing 60mph on a long straight with good visibility.
-Meanwhile the mongs who make driving on country lanes so dangerous will continue driving to the limit, not the conditions, and hence continue taking blind corners at ~40-50mph, because it's 'under the limit', which still means you're stuffed if you meet one coming 'round a corner. Likewise if someone pulls out of a badly designed junction and gets broadsided at 50mph, as opposed to 60mph, the outcome is still pretty similar.
-In other words rather than spending money on better junction layouts where possible, reducing only dangerous areas to 50mph and educating idiots that driving to the conditions and the road you can see is far more important than the limit the government instead has gone for the option that puts money in their pockets.