This would be a lifesaver while developing my modpack. Running /reload takes around a minute and I don't have the time to stare at Minecraft until it finishes.

A couple months late to get to this, apologies.

I've had a quick look into this and the large issue is with how /reload is primarily a server-sided command. The server reloads all the data packs and then updates what it needs to the client once it's done. I'm not entirely sure when or where would be the best spot to hook in, and even then, I'm not sure it's the best idea to do so, especially when /reload isn't likely a command that people execute often unless like in your case, a mod pack.