Current modern stadiums will need the stand they want the safe standing in to be essentially scraped out and reconfigured to allow the required incline neeeded for safe standing, like the emirates will for example, but the lower glwadys was originally a terraced stand so may be able to just have the rail seating installed?
The current design dimensions at BMD show it to be extremely tight for essentially doubling the safe standing capacity, I think they're telling us we could increase it by ten thousand to get less objections from fans tbh.