I'm not happy that all the money I spent on Traitor Legions and the Gathering Storm books has been a big waste of time. Bit of a d**k move but hopefully the edition will be worth it.
There's theoretically nothing stopping you from continuing to play 7th edition, also, 8th edition has been in the rumour mill for like 2 years now. It'd be a bit naive to rule out any possibility that things might not port over. GW have done it before with 2nd to 3rd edition so there's even a precedent. For myself, I mostly picked up Gathering Storm for the storyline. I'm a bit sad that Traitor Legions isn't going to port over but I'm hoping there will be an 8th edition equivalent at some point.
Personally, I'm looking forward to the alleged streamlining they keep promising us. Doubtlessly there will be some changes that I don't like because they mess elements of my army up but equally there will be other mechanics that I can take advantage of to leverage the system against my opponents. As far as mechanics go, I don't think it'll be better or worse per se, merely different and there's going to be some adjustment required. I for one intend to embrace the change (hail Tzeentch!) rather than complain about it, if nothing else it'll give me a head-start over the players that don't.