SUNSfan raised a couple of good points that I agreed on, which I would summarize as the following:
1. DOTA 2 arguably has the largest barrier for new players to enter to, especially ever since 7.00 came out with the Talents system. Put yourself in a new player's perspective, that I assume has a minimal knowledge of MOBAs (5v5 team game, one guy controls one hero, one hero usually has 3 normal abilities and 1 ultimate, goal is to push and destroy the enemy's base), and watching pro players play and not understanding why are they doing things, what does a skill do, and especially during "hype" moments, new players won't understand why a play is so hype and what the hype is all about, which something that kills the experience for many people. I feel that a "newbie stream" would really help alleviate the steep learning curve that DOTA 2 has, especially with the new talents system that complicate the game even further.
2. It can open up opportunities for new, upcoming casters or DOTA 2 personalities. Take, for example, 2 people casting the newbie stream, one as a guy from the casual scene like Baumi, and one is more of an experienced player, but quite well known, like, I dunno, Torte De Lini? Or maybe make it a student-mentor relationship between the two casters like Day9 and Purge so that Day9 will act like the student and Purge will explain as things go on. Though Purge probably won't be up to doing this segment again as SUNSfan explained in the video, so we'll have to find another guy to do it.
3. SUNSfan's model for this stream is what I really like the most from the video, and it fixes some of the problems with the TI4 stream as well, which is repetitiveness and explanations get stale after a while. Having the live lineups prepared on the stream so people can learn as they watch is really useful, as most new players don't know half of the hero names in DOTA 2. Having a third guy answering live questions from Twitter (I'm not gonna say Twitch chat cuz I think its just gonna be memes) will also help in steepening the learning curve that the game has
I feel that the newbie stream has a lot of potential and Valve would be missing out an opportunity if they didn't make one for this year's TI. I don't see why budget would be an issue as it wouldn't cost as much as, say, having Virtual Reality holograms on the main stage.