I would prefer to move to something open source. E.g. riot (https://about.riot.im/) which is built on matrix (https://matrix.org/docs/guides/faq.html#what-is-matrix). Unfortunatelly, it doesn't have threads yet (https://github.com/vector-im/riot-web/issues/2349) but they are not that much used on Slack anyway (also unfortunatelly - as one cannot subscribe to responses on some interesting messages). I am not using Riot (or anything else built on matrix - as nobody I know uses it). So don't ask me for details. Also purism wants to use matrix for their phone which should be shipped in early 2019 (https://puri.sm/shop/librem-5/) so maybe it will help with matrix features... (it's not mainstream phone though, so it's not like every other person will have it).