[darkpuma]

Very little of that is a problem in practice, and proprietary systems like AIM had more than their fair share of problems too.

>no support for threads

That one's just wrong. You can make a threaded client if you want one, although it's not totally clear why you would since the CPU load of IRC is going to be very low in any reasonable situation.

Edit: Oh I see, threads as in forum threads.... just open a new channel. Otherwise, the concept seems to map poorly to ephemeral real time discussion. This is the first I've ever heard of AIM,etc of having forum threads.

[IshKebab]

Slack-style threads work very well for real-time discussion. It's far easier to follow a channel with them than without.

Opening a new channel wouldn't work for fairly obvious reasons (nobody would be in it, you'd effectively have to do it for every single message, etc.).