Why this suggestion wouldn't work out if implemented:
-There is no coal rank, therefore you would be unable to 'share' your iron rank
-Lapiz rank is £25, whereas iron rank is only £10. Despite the fact that you're turning one rank into two, players are still far better off just buying two iron ranks, since it's more beneficial to them.
-Gold rank is £40. Unless you're going to 'share' your rank with three other users, there's no possible way of dividing gold rank.
-Diamond rank is £70. Unless you're going to 'share' your rank with six other users, there's no possible way of dividing diamond rank.
-Emerald rank is £100. Unless you're going to 'share' your rank with three other users, there's no possible way of dividing Emerald rank.
-Obsidian rank is £150. Unless you're going to 'share' your rank with five other users, there's no possible way of dividing Obsidian rank
-Most players that purchase a rank are purchasing it for their own use. If they want to buy their friends a rank, they would do so.
-Players could purchase Obsidian, gain access to its cosmetic perks and then 'share' their rank
-Ranks are there for purchase for one's own use. If this was not the case, players would be able to share their ranks already.
Sorry, but I cannot see this suggestion working out in any way.