If you use the browser client, you should be able to make a simple Greasemonkey script to replace the default text input. Might save some time in the long run.
I guess someone like me could make a browser add-on, too. Though I don't know how many people use the browser client vs. the app.
If you run a proxy you could also block those requests.
The ability to roll your own Slack Client would be great thing imho. I really don't like the default UI (which is also the same layout as all the web based messaging apps, like it's somehow a good thing). I 100% happy with a small window with an IRC style layout - it's a shame I can't use slack (+whatsapp, +messenger) like this.
I guess someone like me could make a browser add-on, too. Though I don't know how many people use the browser client vs. the app.
If you run a proxy you could also block those requests.