yeah you’re going to run out of things to do on retail unlike classic which has unlimited things to do like farm gold… do battle grounds and speedrun mc…
lots of content over here you guys are right 
You have plenty of time to start doing, here’s a short list of things you can do that you can’t do in classic:
- Transmog
- Pet Battles
- Mount Farm
- Rated BGs
- Arenas
- Normal, LFR, Heroic and Mythic raiding difficulties, you can choose what level you want to play.
You have a sub that gives you both, there is very little reason to hamstring yourself to playing only one. They are both great, I enjoy both but retail has a tonne more things to do.
Best suggestion is to ignore the malding classic die-hards who think it’s only possible to play one iteration, they are worried you’re going to leave and never come back.
yeah don’t listen to this guy, he hasn’t done any 8.2 content. Frankly his entire post was a disaster.