Redditor/Guardian DefiantMars made a very detailed post talking about the thematic and lore basis there is for Sunsinger to have support options.
The gist of it is that in Grimoire and quotes and such, Sunsingers are said to be guiding beacons, full of Light and hope and warmth and having the ability to gift power to others.
The subclass does not really reflect this though. This is why I have reimagined the subclass with a few goals:
Make Sunsinger a true support class, keep its current mechanics mostly intact, make it more viable in PvE and PvP, give it more versatility, but also keep it balanced.
Thus I will list the changes I would make. If I leave anything out, it's because I didn't change it.
Solar grenade: Change the name to Solar Flare grenade for pete's sake. The name of a grenade should not be the exact same name as its element. No other changes.
Firebolt: Damage increased to its old value of 97, activation delay improved to Year One levels.
Firebolt was never OP, what made it OP was the old Viking Funeral. Since VF is not returning to that state, Firebolt should not be so weak and hard to land. (It still has a smaller blast radius than it used to, remember. And for the record I think the delay on Arcbolt shouldn't be there either.) Plus this change makes Firebolt a worthy choice of grenade even if you don't have Touch of Flame, which isn't true currently.
Solar Wind: This has never been useful for anything other than trolling your own team. Thus I'm changing its name to Flash Point and its effect will be to temporarily blind the foes it hits.
I don't see this as OP since, if it was, Purifier Robes would be OP but those are seen as a joke. Its biggest utility would be in PvE when there's a very strong sword Knight/Captain or something charging you.
Radiance: The base effect of Radiance (50% damage reduction, much faster cooldowns) is staying the same. However depending on the modifier you choose it will buff your nearby team mates in some fashion.
Song of Flame: Your nearby allies have faster cooldowns, and improved Recovery and weapon Handling.
Song of Flame is the only current "give power to your allies" skill that Sunsinger has and it's so underwhelming. By granting nearby allies something like +3 Recovery and Ophidian Aspect-like Handling and reload speeds it will become a lot more useful for when you group up and attack en-masse.
Radiant Skin: Incoming damage is reduced. When activated, nearby allies receive a temporary Flame Shield.
The ability to give a Flame Shield is a one-time effect that only works if you're close enough when Radiance is activated, and those gifted Flame Shields will last 7 seconds instead of the usual 15 like the Sunsinger's.
Fireborn: If activated from beyond the grave, you are returned to life and Radiance has a shorter duration. The shields of nearby allies continually recharge when not taking damage.
Fireborn simply shouldn't have a short duration if you activate it while you're still alive. I can understand sacrificing duration if you self-rez, but right now you sacrifice duration even if you don't self-rez! Kinda silly if you ask me. As for the shield-regen ability, it will regen at the same speed that Force Barrier does when you choose the Unbreakable skill; if you stop taking damage for a moment, it will slowly refill.
Viking Funeral: Enemies that you Ignite take increased damage from all sources for a short time. Stacks up to 2 times.
The current VF stacks from 5 to 15% but only works when they are burning, which is only like 3 seconds. This makes getting any meaningful length to the debuff impossible unless you're spamming constant grenades into the enemy with Radiance. I want VF to have some utility when NOT in Radiance.
Thus I'm changing it so one stack is 7.5% and the second stack is 15%, and the debuff lasts 7 seconds (look at all the 7s I'm using in my changes, Bungie!). This gives your fireteam some reasonable time to take advantage of the buffs even if you're not using your Super. To illustrate when the debuff is active it will have the same visual effect that Suppressor and Melting Point does over the enemy's head.
So while VF will no longer make you burn for 10 seconds like it did in Year One PvP, it will at least make your defenses a bit lower for a little while. Enough to matter but not enough that it seals your fate either. Touch of Flame is still only 5 ticks of damage and your enemies can't take advantage of the debuff if they don't hit you.
Angel of Light: Aiming your weapon while airborne holds you in place for a short time. Radiance has a larger radius for your allies and your gifts last longer.
Seems kinda odd that ANGEL of Light does nothing but a niche little hovering move, right? I don't really know how large the radius of Radiance should be, with or without Angel of Light, but that last part of "gifts last longer" would let Radiant Skin gifted Flame Shields last 10 seconds and with the other Radiance modifiers, you would keep the buffs for 7 seconds even after you left the radius of the Sunsinger. (So even if you got too far from Song of Flame, you would continue to get the buffs to Recovery and Handling for 7 seconds.)
Let me know what you think. It kills me that Sunsinger is pretty much relegated to "Self-rez and two Fusion nades" for most content. One of those two things are usually the main reason people pick up Sunsinger in this day and age, and it's saddening.
Granted, these are just ideas, not anything final, and I also dreamed up stuff like this back in the old metas where, you know, special weapons actually had a place in PvP. But still, going forward into Destiny 2, assuming Sunsinger returns, I'd rather it be something more like this.