This (the use of big and/or colored text) is just plain bad UX and an obvious abuse of something that needs to be fixed.
With the number of high priority issues IMC is tackling right now, this probably is somewhere a bit down the pipeline so banning people to serve as a lesson for others appears to be the temporary solution.
Also, this issue is clearly covered by TOS’ ToS:
You need to report any game errors, bugs and other game play issues to IMC Games. You shall not abuse them for your own benefits nor to cause grievances to others, and pass this information to others who may abuse them for their benefits.
I’ve been trying to warn people about this and PM those I found in-game about the possible consequence of what they’re doing. Whether they oblige or not is up them.
If you even tried to reason that…
“… THIS DOESN’T AFFECT OTHER PLAYER’S GAMEPLAY!”
It actually does, and if it goes unmitigated everyone else will want to use it because their shouts, party invites and shop names wouldn’t noticeable in the flood of huge colored texts others are using.
If this was meant to be a feature, we would have been informed beforehand. It would have been simply usable from the game’s UI.
This is simply an exploit, and an apparently bannable one.