I haven't looked at the config/set one up since HL1 days so here is a relevant article to how you would set that up https://support.steampowered.com/kb_article.php?ref=1990-UAV... and I am sure there is an equivalent one for source/hl2 games. It lets you set things like delay and so on and I remember it being relatively straightforward.
Basic guide here: https://www.reddit.com/r/GlobalOffensive/comments/2arae2/how..., might be slightly outdated.
However, the swapping players from spectators would require them to directly connect into the game server, and simply spectate from there. I believe you can set them as coaches to prevent ghosting, as spectating directly from the server doesn't allow setting any sort of delay.
So the thing holding esports back is not enough barriers to entry?
Then why have none of the most successful esports had this characteristic? A characteristic they have all shared however, is a simple, out-of-the-box online multiplayer experience.
Archiving old games is an entirely seperate concern.
While esports has gained a little bit more traction since then, my suspicions are aligned with the article, it’s mostly due to dumping massive venture capital into hyping it. And it seems to have hit a wall.
I bet, if they want to move beyond the wall it has hit, one of the key moves will be to start implementing those features discussed above, which will foster the communities which will allow those organic communities to form.
Other than subbing in players, most source games have all of these features. Not sure about Dota 2, but certainly CS:GO and TF2 have all those features with a community that uses them.