I haven't seen anything mentioned about this, so I'll ask these 2 questions here:
1. If an update to tModloader becomes available, will we be able to halt the update to it and still play Terraria untouched in order to keep our worlds from constantly breaking any time tMod updates?
2. Will it be easy to halt each individual mod update until the user wants them to be installed?
It sounds like all downloads/updates will occur within Terraria's in-game mod menu, rather than on Steam out-of-game -- that's very good news. One thing that really worries me about mod support being tied to Steam, is the fact that Steam (in most recent years) makes it near-impossible to disable various game updates and still play said games untouched.
The best thing with not having any mod support is that when a mod updates, there was no worry of a mod updating without your knowing or consent, then completely breaking a current world you're playing on. If mods are integrated into Steam itself in any way as separate downloads outside of Terraria, this could go very badly... between tmod updates and updates to mods themselves. Modding with other games on Steam can sometimes be a nightmare whenever mods update or the games they're played on update, because you're often times forced to break your modded games on Steam because of poor handling and not allowing to halt updates. I love modding this game, but part of the reason I love modding Terraria is because it's been relatively without any headaches in my experience -- it would be unfortate to see this integration add new frustrations occurring endlessly. Hopefully it's all happening in-game, and updating mods is more or less like it always was.
This one big concern aside, I'm extremely happy about this!
1. yes (it's a steam option)