Getting a single 2080 or 2080 ti and selling your current card would be a much better use of your investment dollars. SLI is not well supported anymore, and in some cases, isn't supported at all in a lot of games. Takes extra resources to optimize profiles for SLI for games and since most single card solutions are strong enough now for pretty much most common resolutions and settings, developers feel little need to provide optimizations for configurations that will rarely be used anymore.
Plus, a lot of games even when they are optimized somewhat, don't scale well with a second card anyhow.
I believe you are MUCH better off with any single card solution that will do what you need it to do.
Not to mention 1080 SLI requires a really...