Is it only being removed in 3s, or from the entire game? I'd like to make sure I have the facts straight before I go off the deep end.

It needs to be removed. Played a rank game where they had a 12/1 fiora. Kept triple teaming us and acing. I was teemo, bought thornmail, shut her down. She couldn't touch us after that. They won, barely, but not directly bc of her in team fights anymore.

What are the shining examples of item design from older items (Stuff that S2 began with)?

lol 3 best items for reducing ADC damage are all bad examples of items design huh.
AR pen gets stronger and all the slot efficient AR is badly designed. i want a 300 AR item next season then dont care about the cost i just need a higher AR item for my manaless tanks. not like we can stack sunfire's for slot efficiency anymore

Devil's advocate would say that Veigar's ult would tend to shift a mage from a ratio reliant build to a spellpen reliant build rather than just countering all AP champions. Veigar in general needs some love... he does decently sometimes, but I'll never forget the pro game I saw where 50+ minute hyper farmed veigar got no kills in a teamfight because he was forced to burn his combo on a full GA team... some late game huh?

Also, for people saying to build Maw to counter it. Maw does horrendous damage, and has very mediocre magic resist, costs a ton, and will not actually bring you to a break even point for your lifesteal.

You obviously don't know how thornmail actually works. You need 60% lifesteal to counter thornmail, without including your MR/ARpen or their armor. If they total 300 armor, you would need 120% lifesteal if you had no ARpen or MR. There is no situation where thornmail is not the best armor item for shutting down an AD carry.

You and your ilk simply don't understand how it works. Thornmail is THE BEST counter physical damage item that has ever existed in LoL. They are removing it from TT because they realize that it is TOO GOOD.

Any chance of a new item with similar style? Maybe one with an active that for X seconds you reflect a percent of damage soaked (by AR, MR, or damage reduction skills). It could have a distinct animation for when it is active so you know to switch to a different target, it would still have the problem that some of the scaling depends on your opponent's strength though...just throwing ideas out there.

1. One of the few factors that counters the huge snowballing problem in TT
2. Same as above
3. Makes AP and magic damage have a viable role as it makes 3 bruiser teams unviable

Correct and I think people are also ignoring the cost issue AGAIN which was already stated.

It still scales primarily off of your own power. At the same time, you're comparing a passive, automatic, no-use-required, permanently on damage reflection to a scaling ultimate with a cooldown.

While similar, they aren't parallel by any means.