I've said it before, but I think it's worth re-stating: I think that Psionics needs to have a presence in the Core Rules. It doesn't need to be completely fleshed out, but the base mechanics can be defined in an appendix or something. It is a concept that has been feared by players and DMs in the past because it hasn't been addressed as a core component, even though it has deep roots in the history of D&D.
They have already proven that not everything that goes into the core rules is required. Several things are listed as variant rules. The same could be done for psionics as an appendix.
If it's not addressed now, it will end up being shimmed-in later and it will feel like such. It will end up as a step child of magic instead of a first class citizen where it belongs.