Rail seats are a system that allows standing, in standing areas. There is little reason to use them if you can't stand. What you are seemingly asking for, with safety in mind, is a safety barrier, not rail seats. Its semantics, but if the club were to install rail seats, who's purpose and design is to facilitate spectators standing, in an area where standing is not permitted by regulations, the safety certificate would not be issued.
The south stand is steeper than the sides, so going to the sides if you want steepness is not the answer.
The question is, would you alter the design of the stadium to make the south stand less steep l, so that you can get more standing capacity, when the standing capacity is, by early results, not the most in demand area.
Yes demographics play a part in the purchase patterns, but the fact remains, there was not a massive rush to buy them, but there was for other sections.