This is a pretty bad deal. First, streaming isn't going to be at the same resolution and frame rate. It will be compressed to hell too.
Second, let's pretend that, yes, you need to upgrade every two years. At $35 a month for this service, that works out to $840 EVERY TWO YEARS. That's 1080ti money. And that's only if you think you need a new card every two years. A 1080ti should last you more like 5-10 years so long as you're not extremely picky about running everything at ultra settings that whole time.