I'm fan of the Slayers series too, but I don't know if I disliked Revolution/Evolution-R that much. It did have problems, like being more of a re-hash of the first season instead of having a new villain to face, Gourry not remembering Zel, Amelia and Xellos, although that was probably so that the audience could be introduced to them more than anything else, and one of the more interesting characters they did introduce had a really anticlimactic end, but I still enjoyed it. Granted, I've only seen it once, but I plan on rewatching them after I finish watching Next and then Try to see how I feel about it compared to the other series. Personally, I'd love to see them air the original series and then at least Next. While Next is my absolute favorite Slayers series, I don't think it would be as effective, at least in some parts later on, if people didn't see the first series, the characters' introductions and their interactions with each other to show how they became friends over their travels.
I'm just not sure if they would go for that due to the animation not aging particularly well, although I think I heard that they wanted Slayers on the original Toonami, so that might give them an edge in that regard. Plus, it might be cheaper to go with the older series than with Revolution/Evolution-R. Given their new bumpers and the fact that they have One Piece on the block, they probably don't have as much of a small budget anymore, but they'd most likely go for more affordable over something more expensive. The main selling points for Revolution/Evolution-R for them would probably be the better animation and how people who aren't too familiar with the past three series could still follow along with the storyline. It would certainly help to be familiar with the characters and the first three series, but from what I remember, most people could jump into this one without being too lost, although it wouldn't be the best introduction to the Slayers universe in my opinion either.