Hey samerafach,
1.) I don't see why it wouldn't however you may experience partial potential of the gpu's. 6 cores & 12 threads, it's still alright nowadays but there might be a bottleneck.
2.) Yes, it can.
3.) Well, the newest feature of ray tracing came to the market recently. I don't know what Nvidia has in store for the next generation but then again, it's impossible to keep up graphical processing unit's technology. I'm thinking Nvidia will continue expanding the ray tracing feature, while upgrading their gpu's every 2 years or so.
4.) Titan RTX is a monster of a card. It's very expensive but you maybe assured, you will encounter the best of the best there is to offer from the world. Anyhow, if you have the budget, why not engage your idea of 2 Geforce 2080Ti's in SLI? You won't regret it.