Netsplits apply to networks, not gateways. From Slack's perspective, supporting IRC is relatively simple: send messages in UTF-8 and "send" files by sending the URL that Slack's uploading service produces.
IRC does have a lot of deficiencies, but they're well-understood and the client environment has adapted to them.
IRC does have a lot of deficiencies, but they're well-understood and the client environment has adapted to them.