Choosing an alignment will have mechanical impact on characters. Examples: Spells affect certain alignments and not others; Classes and Subclasses will have alignment restrictions.
7th edition will come when the reboot the D&D movie series (source of 6th edition). By that point all movies will by Bollywood dance movies, so watch out for the power of the college of dance bard (dex casting for the win). Also the 4th pillar will be romance.
7th Edition will go back to the halcyon days of 5th Edition which everyone will be nostalgic for by then.
So overpowered Rangers will be dialled back. The Nova striking Paladin will return and skills we be reduced in power so that DMs no longer have to worry about PCs trivialising their encounters by constantly succeeding at things they try to do.
Also Bards will be returned to being full casters again as Gygax obviously always intended.
The Half-Orc will once again be returned as option alongside the full Orc which replaced it in Fifth Edition. Similarly Half-Elves will return as a full race and no longer just a feat. Ancestries will go back to being called races.
All the 6th edition character classes and races will be included in 7E bringing up the total number of both to a round 20.
6E's elaborate domain management rules won't be in the DMG this time as surveys found that most groups never actually used them.
The special theatre of the mind rules from 6e will be replaced by the more classic grid oriented rules as Grognards never really grokked them and just tended to confuse new players by using grids and minis anyway.
Well, traditionally, the first thing the odd-numbered editions try to do is to fix the previous even-numbered edition's flaws. So in order to create 7th Edition, you simply need to read every single 6th Edition thread, mine them for the most terrible suggestions, and then create rules that are their exact opposites. These will form the basic building blocks of 7th Edition.