Shurelya -> mejai -> zhonya's is kinda hot in comps where you know you can keep mejai stacks alive.

I like zhonyas in general, I think that being tanky on Sona is really underrated.

It's either: - enemy tries to kill your adc, you peel with your choice of (W-chord, R, heal/shield, 2nd W-chord, heal summoner, shurelyas), adc lives and you win game - enemy tries to kill sona, you are tanky and live, or you're tanky and die but enemy had to expend a lot, adc lives and you win game

tl;dr click zhonya win game

There definitely are a lot of fights where the enemy team just tries to kill you and being tanky on sona feels good. Idk if I personally would keep the mejais stacks though. But the zhonyas click does feel really good.

Also shurelya's/defensive items are definitely good for letting you peel, but also for engaging and running enemy champs down

And the item slots are the killer too with dark seal/tear/boots, you can only get one of them or you're stuck sitting on up to like 1800g for zhonyas completion (1 support item, 2 shurelya's, 3 stopwatch, 4 fiendish codex,then pick 2/3 of dark seal/tear/boots)

more thoughts on this I love having stopwatch every game - there's always a karth r or insane dive or something where they try to kill the sona - but without tear or presence of mind I go oom every game

Do I ever go tear/boots early with this build?

idk this is sort of the problem - early boots and maybe lucidiy seems good, tear if not early at least once you have shurelya's seems good, but you don't have enough item slots with stopwatch...maybe if you don't think going zhonya's is worth this game you could sell broken stopwatch to get the slots for boots + tear into seraphs