I've heard fans suggesting that WotC will not bring back Spelljammer and also that (in the unlikely event that they do bring back Spelljamme they will change it). The way that Mike Mearls talks makes it clear that he is not intending to throw away the crystal spheres or the Phlogiston.
Mentioned in these videos:
- The mind flayers used to have a spelljamming empire that spanned most, if not all of the crystal spheres,
- The illithids are the first race to have a spelljamming empire,
- Illithids are powerful, but they are really just the tools of the elder brains,
- Gith smashed the mind flayer empire (and the githyanki and the githzerai hunt down and kill any illithids that attempt to reorganise),
- Individual elder brains attempt to come up with plots that will allow them to reestablish their lost empire,
- Nautiloids may be one of the oldest ship designs in the Spelljammer universe (the illithids may be the oldest race to learn how to spelljam),
- Nobody knows how Gith destroyed the illithid empire. The mind flayers don't talk about it, the githyanki and githzerai don't talk about it and even the gods don't talk about it,
- Gith's followers split into the two factions we know today after the illithid empire was destroyed,
- Gith went to Hell (seems like they renamed the Nine Hells) to strike a deal with Tiamat, and never returned,
- Vlaakith returned in Gith's place and told her followers that she had been sent to lead them until Gith returned,
- Some red dragons have been ordered to help the githyanki.
- The service that red dragons provide to the githyanki interfers with their usual ageing process, and therefore stops them growing into larger dragons (so this service is a big deal).
My main line of thought now is: Will WotC use the illithids (and their nautiloids) and one or both of the gith races as the framing mechanism for one of the upcoming 2018 D&D products?