This probably won't help you that much (

) but, here are my thoughts.
The S20 is a solid platform, especially at the price point that europtic is selling them at. However, the barrel lengths are long for use with a can, which is seems you will be using based on your comment about threading the Tikka. A lot of the other major components (barrel, action, trigger) are compariable, or even the same (barrel) as the Tikka.
That being said, I think that the Tikka will leave you with a better platform to eventually get what you want out of the rifle. However, who knows when they will actually start shipping. It seems that Tikka does a better job at getting new products to shelves than others (I am looking at you Ruger, who promised a .22 ARC in the American G2 in 1Q and it is now June), there is still no guarantee. If this is something that you want to hunt with this fall, then the S20 is probably your better bet. You could get it, and then when the Tikkas finally do show up, sell and buy the Tikka. If it is just something you want in the stable, then maybe wait for the Tikka.