Support leveling and gold gen can improve still

For gameplay there really isn't anything that can be done to improve it any further, a lot of supporting is a babysitter for your team in the sense of protecting them and engaging for them. Some APC carry supports have managed to get into the role also for those who want to be the damage dealing playmakers on their team, only way to improve on that front is to find ways to make room for other carry type champs to go into the support role.

Issues that have plagued support itemization is that either they are too good and used by others outside of support (been seeing a lot of tanks run with redemption+locket) or they suck but are cheap so the best option supports have with their lower gold income. Nothing is really wrong wrong with tank and support itemization overlapping since they can both often play a similar role for their team of protect and/or engage. Improving the gold income of supports will allow the support items with actives to have the cost of some of the support items increased a bit without targeting their active effect values.

Leveling is also an issue for supports. Since they are supposed to make sure their team members are getting the kills and farm similar to gold they will only get the assist exp on unit and champ kill.

Fixing the exp issue I think can be fixed or at least mitigated I think by giving a 10% bonus increase to assist exp for unit and champ kill (random number picked out the top of my head) to all the gold gen items.

The gold and exp issue can be further improved through sightstone. Give it an effect of increasing their bonus gold gen (basically everything outside of unit/champion kill gold and base passive gold gen) and exp gen by 50% (again number pulled out the top of my head). This way supports can get properly rolling along with the rest of their team mates, while the carry supports that like to ignore getting sightstone will get effectively punished by not leveling as fast as their team members or opponent support or get as much gold (don't build sightstone and you will put both your team and yourself behind).