I main support, and so far this season has been incredible for supports. We've a a slew of new items, new amazing masteries and a ton of QOL changes, and Im here to suggest one more.

Sightstone is a great item. For 700 gold we get an item that gives us a constant supply of wards all game long. We only need to place a measily 6 wards to make our money back from it, something we do after 9 minutes most of the time. Even the ruby sighstone is so gold efficient that we can basically upgrade it straight away for no loss. My problem is, for an inventory slot it just doesnt give us enough wards.

3 wards from the ruby is great and all, but 3 wards is never sufficient for map coverage. That dragon, baron and one other spot. Really insufficient late game. We will always have to be buying 1-3 extra wards to get the coverage we need, devoting two inventory slots to wards. So with boots, sighstone, a gp10, and wards (the bare essentials for a support), we have 4 slots filled. Now, adding aegis and thats 5 slots, one left for a single component on our next item. And thats not including pink wards, or an oracles that we know we cant use right away. So if it has multiple excellent components then we can only fit one of them, and any additional gold we had at the time might aswell not be there on that trip back to base. Its awkward and is really getting on my nerves in an otherwise fun season.

My suggestion is simple: Give use another upgrade to sightstone that gives us 5 wards. Make it only cost effective mid-to-late-game to prevent ward saturation bot lane. Something like build from a giants, or one of the other small support items like mana manipulator, or even from a gp10, like kages or philo. Im sure you could find some way to make it work. Its really just a QOL change that i think I and a lot of other supports would be very grateful for.

PS: thresh is awesome and really cool to play, little awkward with his E, but practice irons that out.

The thing is that not only the supp should buy wards.

I buy sightstone quite often on mid/jungler too if i see that my team doesnt buy enough wards. I think its fine as it is.

I like the idea of more variations that have different active limits and total usages with a logical upgrade structure that allows you to go in either direction. Say you could upgrade from 2 too 3 to 4 active, and from 4 to 5 to 6 usages. If every combination was available that would be up too 9 types which would naturally culminate at 'Diamond sight-stone' with max active and max usages, the others would have various gem type names 'Emerald sight-stone', 'Pearl sight-stone' etc etc. With more modest costs to upgrade each level it's something that can scale with more granularity and is thus easier to use.

I main support also. I love the Sightstone. It's one of the best items, in my opinion, during laning phase. However, I never rely on just the Sightstone for wards. 2 or 3 is just not enough. I always keep another slot full of wards. As long as you use your Sightstone wards first it's still the most efficient gold wise. You're still saving money while maintaining the same coverage you would without it.
My standard build is something along the lines of Sightstone, Wards, Boots, Shurelias, and 2 others which depend on the enemy team. Later on I'll sell the Sightstone to make room for a 5th item while keeping my 6th slot for 5 regular wards

*Edit* I think that making the sightstone upgradable to to place more wards might end up just a little too efficient. Definitely too "Easy Mode" for Supports.

1. Sightstone is a trade-off. Just like G-10 items you are trading power for cost efficiency. Just like G-10 items they are taking up a space that could be filled with stronger items. At some point in the game you are supposed to sell/upgrade these items to free up space for more powerful ones. Again, it's meant to be a trade-off which might explain why it feels awkward to you.

2. Junglers are also responsible for warding. If he isn't pitching in then kindly ask him to. I see many junglers who get sightstone if they don't build lantern.

Yea many junglers build (or at least should) build a sightstone.
6 wards late game + a few extra vision wards from various members is usually enough to ward the river and either your or their jungle extensively.

I'd been using it for a while, but the loss of a normal slot can be more problematic than it's worth, especially in these lower tier games where the players have a tendency to just gather up mid and rush.

I think it's fine as it is, for more upper tier play. For less organized teams, pick ups especially, it seems lacking. Nothing you can really do about that, though.