I thought so, as well. But, i don't think the Botani's model is suited for playability (the lack of armor). They can't be neutral because the Breakers already joined the Horde alongside the Mag'har. Now, i don't say they would become allied races, but the Horde and Alliance, each, would definitely push to aid one of these two factions in their conflict.
On the other hand, i agree with the Shadowlands races becoming playable.
Since the Saberon were intentionally left relevant (along with the Botani), and the fact that they are based on the Worgen skeleton and that they can wear armor, i believe they would become an allied race at some point (for the Horde, as they are tribal).
I highly believe the Mogu would become playable. Even though their model wasn't updated, a faction of them (the Rajani) joined us in 8.3, and since they are based on the Draenei skeleton it wouldn't be so hard to adjust it. It makes the most sense for them to join their old Zandalari allies in the Horde (and because they are cruel and ruthless like the Orcs).
I think they it is more likely that they would add the Ankoan, rather than the Jinyu, alongside a Blademaster class.
Although i would very much like to see Hozen become playable, i don't know if their model allows it. Their hands are already used to support their body, which limits their use. Though, they have been seen to be among the Horde ranks in Zuldazar. They would have to introduce an upright Hozen model (like this:
https://hearthstone.fandom.com/wiki/Lotus_Bruiser)
The Mantid, again, would be another cool option. But, i don't know if their model allows it with their extra pair of hands sprouting from their chest and the pair of wings on their back.
The only problem is that there is no way for the Pandaren to leave the Wandering Isle to show us how neutrality works. That would have been very helpful for Triceron.
True. How else would they fit the upcoming Shadowlands races on that list...