1.Tikal is from the past, and she's not Silver, so she can't time travel
2.Knuckles already has a girlfriend, and is involved in 3 other couples, Knuxsu, Knuxouge, and Knuxonia.
3.Knux has only met Tikal a few times, and it was only for a few seconds
4.Tikal and Knux Zeigen no affections for eachother
5.(biggest reason) Knuckles and Tikal are RELATED. So them being a couple, would be like your cousin dating your cousin, it's just plain gross.
6.I don't think they're compatible. Tikal hates violence and fighting, and always works things out in a peaceful manor. When Knuckles always works things with fighting and anger.