Hey! We saw this message and ended up doing a little bit of research as a result. We don't actively have any plans to add subtitles to our videos at this time, but it's not a bad idea. We'll definitely take a look at how feasible it is for us and see what we can do.
In the meantime, I HIGHLY recommend that if somebody is having a hard time following non-visual dialogue in LRHS to follow along in the comic itself at homestuck.com. Each episode of Let's Read Homestuck has information in the description stating which pages the episode covers. Unfortunately, since the conversion from mspaintadventures.com to homestuck.com, the pages aren't entirely accurate anymore, but you can simply subtract 1900 from any page number that starts with "00XXXX" and you should end up approximately in the right area. Alternatively, if you Google "Homestuck [chunk of dialogue from the video]", you'll likely find the page you're looking for that way.